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	$33.77	11.544%	$37.6684	$37.67	$37.65	$37.70
Purchase #2	$179.63	10.868%	$199.1522	$199.15	$199.15	$199.20
Purchase #3	$208.90	12.287%	$234.5675	$234.57	$234.55	$234.60
Purchase #4	$146.37	4.428%	$152.8513	$152.85	$152.85	$152.90
Purchase #5	$137.74	10.189%	$151.7743	$151.77	$151.75	$151.80
Purchase #6	$237.51	7.465%	$255.2401	$255.24	$255.25	$255.20
Purchase #7	$76.92	8.442%	$83.4136	$83.41	$83.40	$83.40
7 purchase totals =	$1,020.84		$1,114.6674	$1,114.66	$1,114.60	$1,114.80