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	$146.79	3.825%	$152.4047	$152.40	$152.40	$152.40
Purchase #2	$40.60	8.823%	$44.1821	$44.18	$44.20	$44.20
Purchase #3	$134.84	12.175%	$151.2568	$151.26	$151.25	$151.30
Purchase #4	$29.82	13.643%	$33.8883	$33.89	$33.90	$33.90
Purchase #5	$134.56	13.178%	$152.2923	$152.29	$152.30	$152.30
Purchase #6	$161.35	11.871%	$180.5039	$180.50	$180.50	$180.50
Purchase #7	$149.74	4.577%	$156.5936	$156.59	$156.60	$156.60
7 purchase totals =	$797.70		$871.1217	$871.11	$871.15	$871.20