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	$129.91	4.761%	$136.095	$136.10	$136.10	$136.10
Purchase #2	$81.92	9.521%	$89.7196	$89.72	$89.70	$89.70
Purchase #3	$140.27	11.152%	$155.9129	$155.91	$155.90	$155.90
Purchase #4	$111.44	12.371%	$125.2262	$125.23	$125.25	$125.20
Purchase #5	$107.33	9.853%	$117.9052	$117.91	$117.90	$117.90
Purchase #6	$165.70	4.822%	$173.6901	$173.69	$173.70	$173.70
Purchase #7	$59.26	4.624%	$62.0002	$62.00	$62.00	$62.00
7 purchase totals =	$795.83		$860.5492	$860.56	$860.55	$860.50