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	$236.61	12.797%	$266.889	$266.89	$266.90	$266.90
Purchase #2	$42.87	6.184%	$45.5211	$45.52	$45.50	$45.50
Purchase #3	$73.39	11.619%	$81.9172	$81.92	$81.90	$81.90
Purchase #4	$98.31	6.377%	$104.5792	$104.58	$104.60	$104.60
Purchase #5	$134.35	13.248%	$152.1487	$152.15	$152.15	$152.10
Purchase #6	$85.98	4.461%	$89.8156	$89.82	$89.80	$89.80
Purchase #7	$146.39	10.713%	$162.0728	$162.07	$162.05	$162.10
7 purchase totals =	$817.90		$902.9436	$902.95	$902.90	$902.90