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	$250.85	9.400%	$274.4299	$274.43	$274.45	$274.40
Purchase #2	$242.96	13.756%	$276.3816	$276.38	$276.40	$276.40
Purchase #3	$74.85	5.851%	$79.2295	$79.23	$79.25	$79.20
Purchase #4	$54.60	13.485%	$61.9628	$61.96	$61.95	$62.00
Purchase #5	$238.34	6.449%	$253.7105	$253.71	$253.70	$253.70
Purchase #6	$88.55	7.462%	$95.1576	$95.16	$95.15	$95.20
Purchase #7	$55.38	7.494%	$59.5302	$59.53	$59.55	$59.50
7 purchase totals =	$1,005.53		$1,100.4021	$1,100.40	$1,100.45	$1,100.40