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	$101.70	3.791%	$105.5554	$105.56	$105.55	$105.60
Purchase #2	$47.85	13.485%	$54.3026	$54.30	$54.30	$54.30
Purchase #3	$34.54	10.785%	$38.2651	$38.27	$38.25	$38.30
Purchase #4	$99.29	11.342%	$110.5515	$110.55	$110.55	$110.60
Purchase #5	$237.39	11.844%	$265.5065	$265.51	$265.50	$265.50
Purchase #6	$35.57	7.800%	$38.3445	$38.34	$38.35	$38.30
Purchase #7	$126.54	7.217%	$135.6724	$135.67	$135.65	$135.70
7 purchase totals =	$682.88		$748.1980	$748.20	$748.15	$748.30