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	$82.58	3.150%	$85.1813	$85.18	$85.20	$85.20
Purchase #2	$131.71	11.530%	$146.8962	$146.90	$146.90	$146.90
Purchase #3	$112.48	13.871%	$128.0821	$128.08	$128.10	$128.10
Purchase #4	$70.38	9.727%	$77.2259	$77.23	$77.25	$77.20
Purchase #5	$151.76	3.557%	$157.1581	$157.16	$157.15	$157.20
Purchase #6	$54.62	10.266%	$60.2273	$60.23	$60.25	$60.20
Purchase #7	$157.29	9.382%	$172.0469	$172.05	$172.05	$172.00
7 purchase totals =	$760.82		$826.8178	$826.83	$826.90	$826.80