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	$155.83	12.372%	$175.1093	$175.11	$175.10	$175.10
Purchase #2	$29.92	11.117%	$33.2462	$33.25	$33.25	$33.20
Purchase #3	$128.96	12.832%	$145.5081	$145.51	$145.50	$145.50
Purchase #4	$208.33	6.679%	$222.2444	$222.24	$222.25	$222.20
Purchase #5	$7.80	11.852%	$8.7245	$8.72	$8.70	$8.70
Purchase #6	$57.46	13.489%	$65.2108	$65.21	$65.20	$65.20
Purchase #7	$159.27	9.593%	$174.5488	$174.55	$174.55	$174.50
7 purchase totals =	$747.57		$824.5921	$824.59	$824.55	$824.40