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	$87.32	12.599%	$98.3214	$98.32	$98.30	$98.30
Purchase #2	$30.76	7.670%	$33.1193	$33.12	$33.10	$33.10
Purchase #3	$140.91	5.693%	$148.932	$148.93	$148.95	$148.90
Purchase #4	$214.57	6.109%	$227.6781	$227.68	$227.70	$227.70
Purchase #5	$18.98	7.154%	$20.3378	$20.34	$20.35	$20.30
Purchase #6	$146.50	9.760%	$160.7984	$160.80	$160.80	$160.80
Purchase #7	$125.61	4.779%	$131.6129	$131.61	$131.60	$131.60
7 purchase totals =	$764.65		$820.7999	$820.80	$820.80	$820.70