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	$28.28	13.187%	$32.0093	$32.01	$32.00	$32.00
Purchase #2	$118.35	9.250%	$129.2974	$129.30	$129.30	$129.30
Purchase #3	$122.35	13.594%	$138.9823	$138.98	$139.00	$139.00
Purchase #4	$109.67	4.313%	$114.4001	$114.40	$114.40	$114.40
Purchase #5	$210.82	13.290%	$238.838	$238.84	$238.85	$238.80
Purchase #6	$236.67	5.755%	$250.2904	$250.29	$250.30	$250.30
Purchase #7	$77.47	10.510%	$85.6121	$85.61	$85.60	$85.60
7 purchase totals =	$903.61		$989.4296	$989.43	$989.45	$989.40