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	$5.48	7.207%	$5.8749	$5.87	$5.85	$5.90
Purchase #2	$183.90	8.272%	$199.1122	$199.11	$199.10	$199.10
Purchase #3	$160.85	7.240%	$172.4955	$172.50	$172.50	$172.50
Purchase #4	$78.45	13.819%	$89.291	$89.29	$89.30	$89.30
Purchase #5	$25.53	8.532%	$27.7082	$27.71	$27.70	$27.70
Purchase #6	$235.43	12.217%	$264.1925	$264.19	$264.20	$264.20
Purchase #7	$37.92	11.782%	$42.3877	$42.39	$42.40	$42.40
7 purchase totals =	$727.56		$801.0620	$801.06	$801.05	$801.10