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	$133.44	4.759%	$139.7904	$139.79	$139.80	$139.80
Purchase #2	$54.83	7.643%	$59.0207	$59.02	$59.00	$59.00
Purchase #3	$239.96	10.220%	$264.4839	$264.48	$264.50	$264.50
Purchase #4	$19.47	13.149%	$22.0301	$22.03	$22.05	$22.00
Purchase #5	$67.56	3.449%	$69.8901	$69.89	$69.90	$69.90
Purchase #6	$99.94	11.373%	$111.3062	$111.31	$111.30	$111.30
Purchase #7	$204.83	12.178%	$229.7742	$229.77	$229.75	$229.80
7 purchase totals =	$820.03		$896.2956	$896.29	$896.30	$896.30