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	$40.48	12.371%	$45.4878	$45.49	$45.50	$45.50
Purchase #2	$146.72	3.224%	$151.4503	$151.45	$151.45	$151.50
Purchase #3	$203.67	12.146%	$228.4078	$228.41	$228.40	$228.40
Purchase #4	$28.31	10.230%	$31.2061	$31.21	$31.20	$31.20
Purchase #5	$15.40	5.654%	$16.2707	$16.27	$16.25	$16.30
Purchase #6	$169.43	10.433%	$187.1066	$187.11	$187.10	$187.10
Purchase #7	$216.53	13.852%	$246.5237	$246.52	$246.50	$246.50
7 purchase totals =	$820.54		$906.4530	$906.46	$906.40	$906.50