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	$7.64	6.202%	$8.1138	$8.11	$8.10	$8.10
Purchase #2	$40.39	12.811%	$45.5644	$45.56	$45.55	$45.60
Purchase #3	$151.88	4.430%	$158.6083	$158.61	$158.60	$158.60
Purchase #4	$216.84	12.834%	$244.6692	$244.67	$244.65	$244.70
Purchase #5	$36.96	10.284%	$40.761	$40.76	$40.75	$40.80
Purchase #6	$111.30	11.690%	$124.311	$124.31	$124.30	$124.30
Purchase #7	$128.44	3.172%	$132.5141	$132.51	$132.50	$132.50
7 purchase totals =	$693.45		$754.5418	$754.53	$754.45	$754.60