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	$72.76	12.617%	$81.9401	$81.94	$81.95	$81.90
Purchase #2	$156.57	6.775%	$167.1776	$167.18	$167.20	$167.20
Purchase #3	$158.70	5.834%	$167.9586	$167.96	$167.95	$168.00
Purchase #4	$6.29	13.793%	$7.1576	$7.16	$7.15	$7.20
Purchase #5	$64.31	13.272%	$72.8452	$72.85	$72.85	$72.80
Purchase #6	$170.51	5.866%	$180.5121	$180.51	$180.50	$180.50
Purchase #7	$66.62	6.474%	$70.933	$70.93	$70.95	$70.90
7 purchase totals =	$695.76		$748.5242	$748.53	$748.55	$748.50