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	$36.69	9.225%	$40.0747	$40.07	$40.05	$40.10
Purchase #2	$39.56	6.718%	$42.2176	$42.22	$42.20	$42.20
Purchase #3	$116.92	6.796%	$124.8659	$124.87	$124.85	$124.90
Purchase #4	$67.95	13.814%	$77.3366	$77.34	$77.35	$77.30
Purchase #5	$63.43	12.699%	$71.485	$71.49	$71.50	$71.50
Purchase #6	$125.53	7.504%	$134.9498	$134.95	$134.95	$134.90
Purchase #7	$147.65	5.380%	$155.5936	$155.59	$155.60	$155.60
7 purchase totals =	$597.73		$646.5232	$646.53	$646.50	$646.50