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	$108.77	13.444%	$123.393	$123.39	$123.40	$123.40
Purchase #2	$70.79	10.600%	$78.2937	$78.29	$78.30	$78.30
Purchase #3	$223.67	7.858%	$241.246	$241.25	$241.25	$241.20
Purchase #4	$31.75	7.794%	$34.2246	$34.22	$34.20	$34.20
Purchase #5	$151.86	5.672%	$160.4735	$160.47	$160.45	$160.50
Purchase #6	$202.65	3.393%	$209.5259	$209.53	$209.55	$209.50
Purchase #7	$107.89	10.832%	$119.5766	$119.58	$119.60	$119.60
7 purchase totals =	$897.38		$966.7333	$966.73	$966.75	$966.70