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	$111.48	11.337%	$124.1185	$124.12	$124.10	$124.10
Purchase #2	$67.34	11.393%	$75.012	$75.01	$75.00	$75.00
Purchase #3	$242.89	3.126%	$250.4827	$250.48	$250.50	$250.50
Purchase #4	$108.67	7.605%	$116.9344	$116.93	$116.95	$116.90
Purchase #5	$50.34	6.519%	$53.6217	$53.62	$53.60	$53.60
Purchase #6	$6.61	11.539%	$7.3727	$7.37	$7.35	$7.40
Purchase #7	$12.53	10.852%	$13.8898	$13.89	$13.90	$13.90
7 purchase totals =	$599.86		$641.4318	$641.42	$641.40	$641.40