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	$43.32	4.369%	$45.2127	$45.21	$45.20	$45.20
Purchase #2	$53.76	6.200%	$57.0931	$57.09	$57.10	$57.10
Purchase #3	$131.88	9.405%	$144.2833	$144.28	$144.30	$144.30
Purchase #4	$103.72	6.625%	$110.5915	$110.59	$110.60	$110.60
Purchase #5	$152.41	13.303%	$172.6851	$172.69	$172.70	$172.70
Purchase #6	$141.46	5.468%	$149.195	$149.20	$149.20	$149.20
Purchase #7	$131.77	6.795%	$140.7238	$140.72	$140.70	$140.70
7 purchase totals =	$758.32		$819.7845	$819.78	$819.80	$819.80