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	$47.77	13.761%	$54.3436	$54.34	$54.35	$54.30
Purchase #2	$71.61	8.167%	$77.4584	$77.46	$77.45	$77.50
Purchase #3	$142.44	4.215%	$148.4438	$148.44	$148.45	$148.40
Purchase #4	$114.34	7.698%	$123.1419	$123.14	$123.15	$123.10
Purchase #5	$75.51	3.790%	$78.3718	$78.37	$78.35	$78.40
Purchase #6	$155.71	6.181%	$165.3344	$165.33	$165.35	$165.30
Purchase #7	$95.81	4.481%	$100.1032	$100.10	$100.10	$100.10
7 purchase totals =	$703.19		$747.1971	$747.18	$747.20	$747.10