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	$228.87	10.610%	$253.1531	$253.15	$253.15	$253.20
Purchase #2	$85.55	10.775%	$94.768	$94.77	$94.75	$94.80
Purchase #3	$53.40	13.224%	$60.4616	$60.46	$60.45	$60.50
Purchase #4	$55.27	11.327%	$61.5304	$61.53	$61.55	$61.50
Purchase #5	$36.39	10.613%	$40.2521	$40.25	$40.25	$40.30
Purchase #6	$70.45	4.824%	$73.8485	$73.85	$73.85	$73.80
Purchase #7	$158.40	8.169%	$171.3397	$171.34	$171.35	$171.30
7 purchase totals =	$688.33		$755.3534	$755.35	$755.35	$755.40