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	$42.32	7.541%	$45.5114	$45.51	$45.50	$45.50
Purchase #2	$128.51	12.689%	$144.8166	$144.82	$144.80	$144.80
Purchase #3	$76.29	12.539%	$85.856	$85.86	$85.85	$85.90
Purchase #4	$132.61	12.718%	$149.4753	$149.48	$149.50	$149.50
Purchase #5	$73.65	7.493%	$79.1686	$79.17	$79.15	$79.20
Purchase #6	$57.64	8.691%	$62.6495	$62.65	$62.65	$62.60
Purchase #7	$57.46	13.109%	$64.9924	$64.99	$65.00	$65.00
7 purchase totals =	$568.48		$632.4698	$632.48	$632.45	$632.50