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	$240.29	6.418%	$255.7118	$255.71	$255.70	$255.70
Purchase #2	$39.94	6.474%	$42.5257	$42.53	$42.55	$42.50
Purchase #3	$170.78	12.375%	$191.914	$191.91	$191.90	$191.90
Purchase #4	$69.67	7.243%	$74.7162	$74.72	$74.70	$74.70
Purchase #5	$60.46	13.319%	$68.5127	$68.51	$68.50	$68.50
Purchase #6	$161.69	13.838%	$184.0647	$184.06	$184.05	$184.10
Purchase #7	$189.77	5.753%	$200.6875	$200.69	$200.70	$200.70
7 purchase totals =	$932.60		$1,018.1326	$1,018.13	$1,018.10	$1,018.10