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	$169.41	11.609%	$189.0768	$189.08	$189.10	$189.10
Purchase #2	$188.41	11.363%	$209.819	$209.82	$209.80	$209.80
Purchase #3	$166.87	4.103%	$173.7167	$173.72	$173.70	$173.70
Purchase #4	$194.34	7.664%	$209.2342	$209.23	$209.25	$209.20
Purchase #5	$49.72	12.454%	$55.9121	$55.91	$55.90	$55.90
Purchase #6	$109.27	7.674%	$117.6554	$117.66	$117.65	$117.70
Purchase #7	$37.45	12.579%	$42.1608	$42.16	$42.15	$42.20
7 purchase totals =	$915.47		$997.5750	$997.58	$997.55	$997.60