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	$99.89	8.334%	$108.2148	$108.21	$108.20	$108.20
Purchase #2	$53.59	11.516%	$59.7614	$59.76	$59.75	$59.80
Purchase #3	$67.52	5.579%	$71.2869	$71.29	$71.30	$71.30
Purchase #4	$63.88	13.188%	$72.3045	$72.30	$72.30	$72.30
Purchase #5	$91.28	10.559%	$100.9183	$100.92	$100.90	$100.90
Purchase #6	$116.57	4.117%	$121.3692	$121.37	$121.35	$121.40
Purchase #7	$76.47	12.371%	$85.9301	$85.93	$85.95	$85.90
7 purchase totals =	$569.20		$619.7852	$619.78	$619.75	$619.80