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	$144.82	11.730%	$161.8074	$161.81	$161.80	$161.80
Purchase #2	$172.67	9.234%	$188.6143	$188.61	$188.60	$188.60
Purchase #3	$155.38	6.868%	$166.0515	$166.05	$166.05	$166.10
Purchase #4	$82.48	9.724%	$90.5004	$90.50	$90.50	$90.50
Purchase #5	$65.64	9.447%	$71.841	$71.84	$71.85	$71.80
Purchase #6	$148.64	11.481%	$165.7054	$165.71	$165.70	$165.70
Purchase #7	$96.96	8.155%	$104.8671	$104.87	$104.85	$104.90
7 purchase totals =	$866.59		$949.3871	$949.39	$949.35	$949.40