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	$72.37	8.479%	$78.5063	$78.51	$78.50	$78.50
Purchase #2	$206.47	13.871%	$235.1095	$235.11	$235.10	$235.10
Purchase #3	$117.46	9.231%	$128.3027	$128.30	$128.30	$128.30
Purchase #4	$36.95	11.390%	$41.1586	$41.16	$41.15	$41.20
Purchase #5	$145.74	9.493%	$159.5751	$159.58	$159.60	$159.60
Purchase #6	$178.83	12.247%	$200.7313	$200.73	$200.75	$200.70
Purchase #7	$28.66	8.810%	$31.1849	$31.18	$31.20	$31.20
7 purchase totals =	$786.48		$874.5684	$874.57	$874.60	$874.60