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	$172.56	12.328%	$193.8332	$193.83	$193.85	$193.80
Purchase #2	$239.40	6.311%	$254.5085	$254.51	$254.50	$254.50
Purchase #3	$37.95	10.739%	$42.0255	$42.03	$42.05	$42.00
Purchase #4	$173.80	10.805%	$192.5791	$192.58	$192.60	$192.60
Purchase #5	$228.67	11.287%	$254.48	$254.48	$254.50	$254.50
Purchase #6	$154.63	6.348%	$164.4459	$164.45	$164.45	$164.40
Purchase #7	$133.73	11.223%	$148.7385	$148.74	$148.75	$148.70
7 purchase totals =	$1,140.74		$1,250.6107	$1,250.62	$1,250.70	$1,250.50