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	$146.68	8.518%	$159.1742	$159.17	$159.15	$159.20
Purchase #2	$172.64	4.591%	$180.5659	$180.57	$180.55	$180.60
Purchase #3	$201.44	8.816%	$219.199	$219.20	$219.20	$219.20
Purchase #4	$145.94	4.325%	$152.2519	$152.25	$152.25	$152.30
Purchase #5	$66.41	8.848%	$72.286	$72.29	$72.30	$72.30
Purchase #6	$76.57	12.194%	$85.9069	$85.91	$85.90	$85.90
Purchase #7	$133.90	13.478%	$151.947	$151.95	$151.95	$151.90
7 purchase totals =	$943.58		$1,021.3309	$1,021.34	$1,021.30	$1,021.40