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	$140.63	8.414%	$152.4626	$152.46	$152.45	$152.50
Purchase #2	$188.37	10.652%	$208.4352	$208.44	$208.45	$208.40
Purchase #3	$173.26	13.217%	$196.1598	$196.16	$196.15	$196.20
Purchase #4	$34.28	9.350%	$37.4852	$37.49	$37.50	$37.50
Purchase #5	$78.53	6.545%	$83.6698	$83.67	$83.65	$83.70
Purchase #6	$53.30	3.165%	$54.9869	$54.99	$55.00	$55.00
Purchase #7	$73.69	9.184%	$80.4577	$80.46	$80.45	$80.50
7 purchase totals =	$742.06		$813.6572	$813.67	$813.65	$813.80