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	$34.97	9.597%	$38.3261	$38.33	$38.35	$38.30
Purchase #2	$99.31	13.329%	$112.547	$112.55	$112.55	$112.50
Purchase #3	$78.78	8.112%	$85.1706	$85.17	$85.15	$85.20
Purchase #4	$87.85	5.785%	$92.9321	$92.93	$92.95	$92.90
Purchase #5	$151.74	8.821%	$165.125	$165.13	$165.15	$165.10
Purchase #6	$46.80	6.551%	$49.8659	$49.87	$49.85	$49.90
Purchase #7	$135.39	3.300%	$139.8579	$139.86	$139.85	$139.90
7 purchase totals =	$634.84		$683.8246	$683.84	$683.85	$683.80