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	$148.93	13.720%	$169.3632	$169.36	$169.35	$169.40
Purchase #2	$59.35	5.281%	$62.4843	$62.48	$62.50	$62.50
Purchase #3	$58.49	4.530%	$61.1396	$61.14	$61.15	$61.10
Purchase #4	$24.56	10.624%	$27.1693	$27.17	$27.15	$27.20
Purchase #5	$120.34	3.762%	$124.8672	$124.87	$124.85	$124.90
Purchase #6	$26.47	4.770%	$27.7326	$27.73	$27.75	$27.70
Purchase #7	$18.26	12.660%	$20.5717	$20.57	$20.55	$20.60
7 purchase totals =	$456.40		$493.3279	$493.32	$493.30	$493.40