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	$81.79	4.131%	$85.1687	$85.17	$85.15	$85.20
Purchase #2	$79.83	3.786%	$82.8524	$82.85	$82.85	$82.90
Purchase #3	$146.32	5.181%	$153.9008	$153.90	$153.90	$153.90
Purchase #4	$166.47	13.154%	$188.3675	$188.37	$188.35	$188.40
Purchase #5	$99.57	11.716%	$111.2356	$111.24	$111.25	$111.20
Purchase #6	$79.44	10.210%	$87.5508	$87.55	$87.55	$87.60
Purchase #7	$232.98	10.355%	$257.1051	$257.11	$257.10	$257.10
7 purchase totals =	$886.40		$966.1809	$966.19	$966.15	$966.30