Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$68.86	13.721%	$78.3083	$78.31	$78.30	$78.30
Purchase #2	$61.78	3.531%	$63.9615	$63.96	$63.95	$64.00
Purchase #3	$232.82	13.591%	$264.4626	$264.46	$264.45	$264.50
Purchase #4	$121.35	5.181%	$127.6371	$127.64	$127.65	$127.60
Purchase #5	$241.89	7.834%	$260.8397	$260.84	$260.85	$260.80
Purchase #6	$131.61	3.800%	$136.6112	$136.61	$136.60	$136.60
Purchase #7	$122.45	4.217%	$127.6137	$127.61	$127.60	$127.60
7 purchase totals =	$980.76		$1,059.4341	$1,059.43	$1,059.40	$1,059.40