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	$42.53	13.764%	$48.3838	$48.38	$48.40	$48.40
Purchase #2	$48.27	5.451%	$50.9012	$50.90	$50.90	$50.90
Purchase #3	$134.46	11.521%	$149.9511	$149.95	$149.95	$150.00
Purchase #4	$175.51	12.178%	$196.8836	$196.88	$196.90	$196.90
Purchase #5	$157.93	9.121%	$172.3348	$172.33	$172.35	$172.30
Purchase #6	$6.60	9.410%	$7.2211	$7.22	$7.20	$7.20
Purchase #7	$240.85	8.490%	$261.2982	$261.30	$261.30	$261.30
7 purchase totals =	$806.15		$886.9738	$886.96	$887.00	$887.00