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	$198.94	12.185%	$223.1808	$223.18	$223.20	$223.20
Purchase #2	$63.39	6.164%	$67.2974	$67.30	$67.30	$67.30
Purchase #3	$146.55	11.148%	$162.8874	$162.89	$162.90	$162.90
Purchase #4	$155.50	11.821%	$173.8817	$173.88	$173.90	$173.90
Purchase #5	$225.29	7.668%	$242.5652	$242.57	$242.55	$242.60
Purchase #6	$247.43	5.507%	$261.056	$261.06	$261.05	$261.10
Purchase #7	$128.87	9.634%	$141.2853	$141.29	$141.30	$141.30
7 purchase totals =	$1,165.97		$1,272.1538	$1,272.17	$1,272.20	$1,272.30