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	$120.30	4.500%	$125.7135	$125.71	$125.70	$125.70
Purchase #2	$226.31	12.375%	$254.3159	$254.32	$254.30	$254.30
Purchase #3	$107.60	3.774%	$111.6608	$111.66	$111.65	$111.70
Purchase #4	$164.37	4.404%	$171.6089	$171.61	$171.60	$171.60
Purchase #5	$63.91	5.472%	$67.4072	$67.41	$67.40	$67.40
Purchase #6	$30.86	9.678%	$33.8466	$33.85	$33.85	$33.80
Purchase #7	$35.42	10.720%	$39.217	$39.22	$39.20	$39.20
7 purchase totals =	$748.77		$803.7699	$803.78	$803.70	$803.70