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	$231.53	8.592%	$251.4231	$251.42	$251.40	$251.40
Purchase #2	$29.71	11.176%	$33.0304	$33.03	$33.05	$33.00
Purchase #3	$142.99	5.255%	$150.5041	$150.50	$150.50	$150.50
Purchase #4	$22.43	13.775%	$25.5197	$25.52	$25.50	$25.50
Purchase #5	$172.66	10.369%	$190.5631	$190.56	$190.55	$190.60
Purchase #6	$181.37	5.226%	$190.8484	$190.85	$190.85	$190.80
Purchase #7	$51.98	8.612%	$56.4565	$56.46	$56.45	$56.50
7 purchase totals =	$832.67		$898.3453	$898.34	$898.30	$898.30