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	$28.82	12.653%	$32.4666	$32.47	$32.45	$32.50
Purchase #2	$153.94	8.599%	$167.1773	$167.18	$167.20	$167.20
Purchase #3	$168.89	11.621%	$188.5167	$188.52	$188.50	$188.50
Purchase #4	$51.94	3.687%	$53.855	$53.86	$53.85	$53.90
Purchase #5	$138.64	12.320%	$155.7204	$155.72	$155.70	$155.70
Purchase #6	$218.78	11.350%	$243.6115	$243.61	$243.60	$243.60
Purchase #7	$9.29	11.567%	$10.3646	$10.36	$10.35	$10.40
7 purchase totals =	$770.30		$851.7121	$851.72	$851.65	$851.80