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	$139.95	11.343%	$155.8245	$155.82	$155.80	$155.80
Purchase #2	$64.68	4.329%	$67.48	$67.48	$67.50	$67.50
Purchase #3	$183.41	12.587%	$206.4958	$206.50	$206.50	$206.50
Purchase #4	$77.34	10.648%	$85.5752	$85.58	$85.60	$85.60
Purchase #5	$39.60	3.871%	$41.1329	$41.13	$41.15	$41.10
Purchase #6	$247.93	10.255%	$273.3552	$273.36	$273.35	$273.40
Purchase #7	$152.40	13.324%	$172.7058	$172.71	$172.70	$172.70
7 purchase totals =	$905.31		$1,002.5694	$1,002.58	$1,002.60	$1,002.60