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	$74.44	12.478%	$83.7286	$83.73	$83.75	$83.70
Purchase #2	$66.57	8.390%	$72.1552	$72.16	$72.15	$72.20
Purchase #3	$73.33	6.105%	$77.8068	$77.81	$77.80	$77.80
Purchase #4	$139.49	10.650%	$154.3457	$154.35	$154.35	$154.30
Purchase #5	$153.36	11.837%	$171.5132	$171.51	$171.50	$171.50
Purchase #6	$53.69	11.693%	$59.968	$59.97	$59.95	$60.00
Purchase #7	$27.64	3.223%	$28.5308	$28.53	$28.55	$28.50
7 purchase totals =	$588.52		$648.0483	$648.06	$648.05	$648.00