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	$134.79	4.504%	$140.8609	$140.86	$140.85	$140.90
Purchase #2	$98.61	6.840%	$105.3549	$105.35	$105.35	$105.40
Purchase #3	$29.78	8.612%	$32.3447	$32.34	$32.35	$32.30
Purchase #4	$131.94	6.824%	$140.9436	$140.94	$140.95	$140.90
Purchase #5	$165.25	4.259%	$172.288	$172.29	$172.30	$172.30
Purchase #6	$153.58	9.140%	$167.6172	$167.62	$167.60	$167.60
Purchase #7	$106.70	12.185%	$119.7014	$119.70	$119.70	$119.70
7 purchase totals =	$820.65		$879.1107	$879.10	$879.10	$879.10