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	$13.60	9.689%	$14.9177	$14.92	$14.90	$14.90
Purchase #2	$90.32	12.385%	$101.5061	$101.51	$101.50	$101.50
Purchase #3	$144.82	10.637%	$160.2245	$160.22	$160.20	$160.20
Purchase #4	$125.71	5.626%	$132.7824	$132.78	$132.80	$132.80
Purchase #5	$29.83	9.310%	$32.6072	$32.61	$32.60	$32.60
Purchase #6	$23.83	8.624%	$25.8851	$25.89	$25.90	$25.90
Purchase #7	$33.28	5.870%	$35.2335	$35.23	$35.25	$35.20
7 purchase totals =	$461.39		$503.1565	$503.16	$503.15	$503.10