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	$124.38	10.400%	$137.3155	$137.32	$137.30	$137.30
Purchase #2	$56.50	5.335%	$59.5143	$59.51	$59.50	$59.50
Purchase #3	$48.76	7.353%	$52.3453	$52.35	$52.35	$52.30
Purchase #4	$163.94	11.126%	$182.18	$182.18	$182.20	$182.20
Purchase #5	$16.29	11.339%	$18.1371	$18.14	$18.15	$18.10
Purchase #6	$130.78	6.607%	$139.4206	$139.42	$139.40	$139.40
Purchase #7	$148.56	7.188%	$159.2385	$159.24	$159.25	$159.20
7 purchase totals =	$689.21		$748.1513	$748.16	$748.15	$748.00