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	$80.50	11.436%	$89.706	$89.71	$89.70	$89.70
Purchase #2	$124.45	7.320%	$133.5597	$133.56	$133.55	$133.60
Purchase #3	$23.27	13.278%	$26.3598	$26.36	$26.35	$26.40
Purchase #4	$92.28	3.179%	$95.2136	$95.21	$95.20	$95.20
Purchase #5	$84.91	5.417%	$89.5096	$89.51	$89.50	$89.50
Purchase #6	$42.95	4.539%	$44.8995	$44.90	$44.90	$44.90
Purchase #7	$125.43	4.628%	$131.2349	$131.23	$131.25	$131.20
7 purchase totals =	$573.79		$610.4831	$610.48	$610.45	$610.50