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	$40.65	5.628%	$42.9378	$42.94	$42.95	$42.90
Purchase #2	$159.52	7.240%	$171.0692	$171.07	$171.05	$171.10
Purchase #3	$163.42	5.718%	$172.7644	$172.76	$172.75	$172.80
Purchase #4	$162.51	10.173%	$179.0421	$179.04	$179.05	$179.00
Purchase #5	$76.71	7.678%	$82.5998	$82.60	$82.60	$82.60
Purchase #6	$183.83	11.622%	$205.1947	$205.19	$205.20	$205.20
Purchase #7	$46.78	7.847%	$50.4508	$50.45	$50.45	$50.50
7 purchase totals =	$833.42		$904.0588	$904.05	$904.05	$904.10