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	$149.29	13.336%	$169.1993	$169.20	$169.20	$169.20
Purchase #2	$121.51	12.618%	$136.8421	$136.84	$136.85	$136.80
Purchase #3	$58.94	4.493%	$61.5882	$61.59	$61.60	$61.60
Purchase #4	$62.57	7.764%	$67.4279	$67.43	$67.45	$67.40
Purchase #5	$164.90	5.204%	$173.4814	$173.48	$173.50	$173.50
Purchase #6	$141.73	8.846%	$154.2674	$154.27	$154.25	$154.30
Purchase #7	$193.47	11.164%	$215.069	$215.07	$215.05	$215.10
7 purchase totals =	$892.41		$977.8753	$977.88	$977.90	$977.90