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	$61.51	6.500%	$65.5082	$65.51	$65.50	$65.50
Purchase #2	$139.75	9.313%	$152.7649	$152.76	$152.75	$152.80
Purchase #3	$129.77	6.296%	$137.9403	$137.94	$137.95	$137.90
Purchase #4	$134.65	8.301%	$145.8273	$145.83	$145.85	$145.80
Purchase #5	$181.31	7.638%	$195.1585	$195.16	$195.15	$195.20
Purchase #6	$98.27	9.138%	$107.2499	$107.25	$107.25	$107.20
Purchase #7	$35.31	13.539%	$40.0906	$40.09	$40.10	$40.10
7 purchase totals =	$780.57		$844.5397	$844.54	$844.55	$844.50