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	$51.75	7.313%	$55.5345	$55.53	$55.55	$55.50
Purchase #2	$34.81	6.677%	$37.1343	$37.13	$37.15	$37.10
Purchase #3	$81.40	11.385%	$90.6674	$90.67	$90.65	$90.70
Purchase #4	$153.78	9.344%	$168.1492	$168.15	$168.15	$168.10
Purchase #5	$5.69	8.233%	$6.1585	$6.16	$6.15	$6.20
Purchase #6	$66.38	8.566%	$72.0661	$72.07	$72.05	$72.10
Purchase #7	$155.54	11.230%	$173.0071	$173.01	$173.00	$173.00
7 purchase totals =	$549.35		$602.7171	$602.72	$602.70	$602.70