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	$128.54	13.811%	$146.2927	$146.29	$146.30	$146.30
Purchase #2	$24.95	4.168%	$25.9899	$25.99	$26.00	$26.00
Purchase #3	$31.84	6.189%	$33.8106	$33.81	$33.80	$33.80
Purchase #4	$81.97	10.248%	$90.3703	$90.37	$90.35	$90.40
Purchase #5	$91.50	8.572%	$99.3434	$99.34	$99.35	$99.30
Purchase #6	$233.76	12.556%	$263.1109	$263.11	$263.10	$263.10
Purchase #7	$11.89	11.471%	$13.2539	$13.25	$13.25	$13.30
7 purchase totals =	$604.45		$672.1717	$672.16	$672.15	$672.20