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	$228.27	11.822%	$255.2561	$255.26	$255.25	$255.30
Purchase #2	$90.97	10.168%	$100.2198	$100.22	$100.20	$100.20
Purchase #3	$219.87	9.129%	$239.9419	$239.94	$239.95	$239.90
Purchase #4	$78.89	8.867%	$85.8852	$85.89	$85.90	$85.90
Purchase #5	$42.39	7.854%	$45.7193	$45.72	$45.70	$45.70
Purchase #6	$140.74	4.294%	$146.7834	$146.78	$146.80	$146.80
Purchase #7	$107.34	11.627%	$119.8204	$119.82	$119.80	$119.80
7 purchase totals =	$908.47		$993.6261	$993.63	$993.60	$993.60