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	$36.51	4.517%	$38.1592	$38.16	$38.15	$38.20
Purchase #2	$53.98	8.493%	$58.5645	$58.56	$58.55	$58.60
Purchase #3	$75.49	12.768%	$85.1286	$85.13	$85.15	$85.10
Purchase #4	$209.72	3.549%	$217.163	$217.16	$217.15	$217.20
Purchase #5	$140.86	13.513%	$159.8944	$159.89	$159.90	$159.90
Purchase #6	$104.52	3.835%	$108.5283	$108.53	$108.55	$108.50
Purchase #7	$61.53	10.256%	$67.8405	$67.84	$67.85	$67.80
7 purchase totals =	$682.61		$735.2785	$735.27	$735.30	$735.30