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	$151.78	12.111%	$170.1621	$170.16	$170.15	$170.20
Purchase #2	$33.47	12.695%	$37.719	$37.72	$37.70	$37.70
Purchase #3	$160.79	7.543%	$172.9184	$172.92	$172.90	$172.90
Purchase #4	$201.60	3.840%	$209.3414	$209.34	$209.35	$209.30
Purchase #5	$6.80	12.168%	$7.6274	$7.63	$7.65	$7.60
Purchase #6	$182.89	11.215%	$203.4011	$203.40	$203.40	$203.40
Purchase #7	$117.56	8.438%	$127.4797	$127.48	$127.50	$127.50
7 purchase totals =	$854.89		$928.6491	$928.65	$928.65	$928.60