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	$172.45	7.358%	$185.1389	$185.14	$185.15	$185.10
Purchase #2	$109.52	13.528%	$124.3359	$124.34	$124.35	$124.30
Purchase #3	$113.28	10.319%	$124.9694	$124.97	$124.95	$125.00
Purchase #4	$66.48	5.678%	$70.2547	$70.25	$70.25	$70.30
Purchase #5	$230.68	12.631%	$259.8172	$259.82	$259.80	$259.80
Purchase #6	$55.85	9.480%	$61.1446	$61.14	$61.15	$61.10
Purchase #7	$171.35	11.635%	$191.2866	$191.29	$191.30	$191.30
7 purchase totals =	$919.61		$1,016.9473	$1,016.95	$1,016.95	$1,016.90