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	$59.93	4.754%	$62.7791	$62.78	$62.80	$62.80
Purchase #2	$50.59	3.826%	$52.5256	$52.53	$52.55	$52.50
Purchase #3	$116.31	7.588%	$125.1356	$125.14	$125.15	$125.10
Purchase #4	$147.28	13.485%	$167.1407	$167.14	$167.15	$167.10
Purchase #5	$154.43	10.673%	$170.9123	$170.91	$170.90	$170.90
Purchase #6	$56.74	5.652%	$59.9469	$59.95	$59.95	$59.90
Purchase #7	$34.83	8.742%	$37.8748	$37.87	$37.85	$37.90
7 purchase totals =	$620.11		$676.3150	$676.32	$676.35	$676.20