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	$96.59	3.120%	$99.6036	$99.60	$99.60	$99.60
Purchase #2	$202.87	5.512%	$214.0522	$214.05	$214.05	$214.10
Purchase #3	$243.73	8.853%	$265.3074	$265.31	$265.30	$265.30
Purchase #4	$152.82	13.726%	$173.7961	$173.80	$173.80	$173.80
Purchase #5	$118.34	4.405%	$123.5529	$123.55	$123.55	$123.60
Purchase #6	$18.60	8.707%	$20.2195	$20.22	$20.20	$20.20
Purchase #7	$139.53	10.396%	$154.0355	$154.04	$154.05	$154.00
7 purchase totals =	$972.48		$1,050.5672	$1,050.57	$1,050.55	$1,050.60