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	$111.54	6.386%	$118.6629	$118.66	$118.65	$118.70
Purchase #2	$12.33	6.165%	$13.0901	$13.09	$13.10	$13.10
Purchase #3	$18.78	6.496%	$19.9999	$20.00	$20.00	$20.00
Purchase #4	$159.72	9.453%	$174.8183	$174.82	$174.80	$174.80
Purchase #5	$69.47	9.759%	$76.2496	$76.25	$76.25	$76.20
Purchase #6	$64.25	13.770%	$73.0972	$73.10	$73.10	$73.10
Purchase #7	$52.69	12.327%	$59.1851	$59.19	$59.20	$59.20
7 purchase totals =	$488.78		$535.1031	$535.11	$535.10	$535.10