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	$107.84	8.489%	$116.9945	$116.99	$117.00	$117.00
Purchase #2	$153.45	12.597%	$172.7801	$172.78	$172.80	$172.80
Purchase #3	$151.94	11.134%	$168.857	$168.86	$168.85	$168.90
Purchase #4	$228.34	9.754%	$250.6123	$250.61	$250.60	$250.60
Purchase #5	$114.81	8.727%	$124.8295	$124.83	$124.85	$124.80
Purchase #6	$146.72	12.644%	$165.2713	$165.27	$165.25	$165.30
Purchase #7	$211.81	5.771%	$224.0336	$224.03	$224.05	$224.00
7 purchase totals =	$1,114.91		$1,223.3783	$1,223.37	$1,223.40	$1,223.40