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	$78.48	5.403%	$82.7203	$82.72	$82.70	$82.70
Purchase #2	$237.82	11.383%	$264.8911	$264.89	$264.90	$264.90
Purchase #3	$204.34	11.358%	$227.5489	$227.55	$227.55	$227.50
Purchase #4	$225.60	9.676%	$247.4291	$247.43	$247.45	$247.40
Purchase #5	$203.54	13.434%	$230.8836	$230.88	$230.90	$230.90
Purchase #6	$137.33	10.575%	$151.8526	$151.85	$151.85	$151.90
Purchase #7	$130.89	11.427%	$145.8468	$145.85	$145.85	$145.80
7 purchase totals =	$1,218.00		$1,351.1724	$1,351.17	$1,351.20	$1,351.10