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	$101.81	4.262%	$106.1491	$106.15	$106.15	$106.10
Purchase #2	$192.85	12.447%	$216.854	$216.85	$216.85	$216.90
Purchase #3	$206.45	9.611%	$226.2919	$226.29	$226.30	$226.30
Purchase #4	$159.57	4.328%	$166.4762	$166.48	$166.50	$166.50
Purchase #5	$80.67	13.479%	$91.5435	$91.54	$91.55	$91.50
Purchase #6	$63.29	11.807%	$70.7627	$70.76	$70.75	$70.80
Purchase #7	$197.90	10.597%	$218.8715	$218.87	$218.85	$218.90
7 purchase totals =	$1,002.54		$1,096.9489	$1,096.94	$1,096.95	$1,097.00