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	$120.85	12.646%	$136.1327	$136.13	$136.15	$136.10
Purchase #2	$38.41	7.158%	$41.1594	$41.16	$41.15	$41.20
Purchase #3	$173.35	13.475%	$196.7089	$196.71	$196.70	$196.70
Purchase #4	$133.89	7.676%	$144.1674	$144.17	$144.15	$144.20
Purchase #5	$35.69	10.164%	$39.3175	$39.32	$39.30	$39.30
Purchase #6	$42.86	13.396%	$48.6015	$48.60	$48.60	$48.60
Purchase #7	$178.25	10.780%	$197.4654	$197.47	$197.45	$197.50
7 purchase totals =	$723.30		$803.5528	$803.56	$803.50	$803.60