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	$81.56	10.634%	$90.2331	$90.23	$90.25	$90.20
Purchase #2	$219.46	6.772%	$234.3218	$234.32	$234.30	$234.30
Purchase #3	$57.29	7.653%	$61.6744	$61.67	$61.65	$61.70
Purchase #4	$180.44	7.473%	$193.9243	$193.92	$193.90	$193.90
Purchase #5	$223.42	5.261%	$235.1741	$235.17	$235.15	$235.20
Purchase #6	$13.40	6.302%	$14.2445	$14.24	$14.25	$14.20
Purchase #7	$152.26	13.143%	$172.2715	$172.27	$172.25	$172.30
7 purchase totals =	$927.83		$1,001.8437	$1,001.82	$1,001.75	$1,001.80