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	$225.85	13.628%	$256.6288	$256.63	$256.65	$256.60
Purchase #2	$185.73	5.438%	$195.83	$195.83	$195.85	$195.80
Purchase #3	$125.36	12.602%	$141.1579	$141.16	$141.15	$141.20
Purchase #4	$45.74	4.271%	$47.6936	$47.69	$47.70	$47.70
Purchase #5	$118.25	11.207%	$131.5023	$131.50	$131.50	$131.50
Purchase #6	$36.64	11.857%	$40.9844	$40.98	$41.00	$41.00
Purchase #7	$20.73	4.597%	$21.683	$21.68	$21.70	$21.70
7 purchase totals =	$758.30		$835.4800	$835.47	$835.55	$835.50