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	$38.52	9.591%	$42.2145	$42.21	$42.20	$42.20
Purchase #2	$34.70	3.736%	$35.9964	$36.00	$36.00	$36.00
Purchase #3	$48.50	12.820%	$54.7177	$54.72	$54.70	$54.70
Purchase #4	$98.31	13.664%	$111.7431	$111.74	$111.75	$111.70
Purchase #5	$200.95	10.194%	$221.4348	$221.43	$221.45	$221.40
Purchase #6	$172.67	8.587%	$187.4972	$187.50	$187.50	$187.50
Purchase #7	$132.53	11.578%	$147.8743	$147.87	$147.85	$147.90
7 purchase totals =	$726.18		$801.4780	$801.47	$801.45	$801.40