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	$66.50	8.143%	$71.9151	$71.92	$71.90	$71.90
Purchase #2	$155.65	11.450%	$173.4719	$173.47	$173.45	$173.50
Purchase #3	$160.69	12.552%	$180.8598	$180.86	$180.85	$180.90
Purchase #4	$52.56	8.619%	$57.0901	$57.09	$57.10	$57.10
Purchase #5	$157.53	5.603%	$166.3564	$166.36	$166.35	$166.40
Purchase #6	$196.98	9.849%	$216.3806	$216.38	$216.40	$216.40
Purchase #7	$11.90	13.306%	$13.4834	$13.48	$13.50	$13.50
7 purchase totals =	$801.81		$879.5573	$879.56	$879.55	$879.70