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	$134.45	9.217%	$146.8423	$146.84	$146.85	$146.80
Purchase #2	$97.44	3.570%	$100.9186	$100.92	$100.90	$100.90
Purchase #3	$220.96	6.539%	$235.4086	$235.41	$235.40	$235.40
Purchase #4	$229.65	6.760%	$245.1743	$245.17	$245.15	$245.20
Purchase #5	$109.63	13.113%	$124.0058	$124.01	$124.00	$124.00
Purchase #6	$32.86	4.619%	$34.3778	$34.38	$34.40	$34.40
Purchase #7	$74.44	5.752%	$78.7218	$78.72	$78.70	$78.70
7 purchase totals =	$899.43		$965.4492	$965.45	$965.40	$965.40