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	$155.27	9.144%	$169.4679	$169.47	$169.45	$169.50
Purchase #2	$59.90	8.488%	$64.9843	$64.98	$65.00	$65.00
Purchase #3	$40.42	5.443%	$42.6201	$42.62	$42.60	$42.60
Purchase #4	$50.53	10.472%	$55.8215	$55.82	$55.80	$55.80
Purchase #5	$13.34	7.822%	$14.3835	$14.38	$14.40	$14.40
Purchase #6	$134.35	10.319%	$148.2136	$148.21	$148.20	$148.20
Purchase #7	$229.33	12.579%	$258.1774	$258.18	$258.20	$258.20
7 purchase totals =	$683.14		$753.6683	$753.66	$753.65	$753.70