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	$187.34	6.123%	$198.8108	$198.81	$198.80	$198.80
Purchase #2	$140.85	10.393%	$155.4885	$155.49	$155.50	$155.50
Purchase #3	$80.77	12.576%	$90.9276	$90.93	$90.95	$90.90
Purchase #4	$38.89	10.198%	$42.856	$42.86	$42.85	$42.90
Purchase #5	$35.98	11.514%	$40.1227	$40.12	$40.10	$40.10
Purchase #6	$152.37	11.313%	$169.6076	$169.61	$169.60	$169.60
Purchase #7	$149.56	10.719%	$165.5913	$165.59	$165.60	$165.60
7 purchase totals =	$785.76		$863.4045	$863.41	$863.40	$863.40