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	$12.29	8.748%	$13.3651	$13.37	$13.35	$13.40
Purchase #2	$179.44	8.846%	$195.3133	$195.31	$195.30	$195.30
Purchase #3	$146.94	3.190%	$151.6274	$151.63	$151.65	$151.60
Purchase #4	$99.57	5.771%	$105.3162	$105.32	$105.30	$105.30
Purchase #5	$90.68	9.618%	$99.4016	$99.40	$99.40	$99.40
Purchase #6	$53.69	10.312%	$59.2265	$59.23	$59.25	$59.20
Purchase #7	$237.48	10.488%	$262.3869	$262.39	$262.40	$262.40
7 purchase totals =	$820.09		$886.6370	$886.65	$886.65	$886.60