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	$124.50	12.132%	$139.6043	$139.60	$139.60	$139.60
Purchase #2	$172.68	13.661%	$196.2698	$196.27	$196.25	$196.30
Purchase #3	$7.80	12.391%	$8.7665	$8.77	$8.75	$8.80
Purchase #4	$173.82	3.382%	$179.6986	$179.70	$179.70	$179.70
Purchase #5	$184.82	13.534%	$209.8335	$209.83	$209.85	$209.80
Purchase #6	$37.75	13.578%	$42.8757	$42.88	$42.90	$42.90
Purchase #7	$146.61	13.104%	$165.8218	$165.82	$165.80	$165.80
7 purchase totals =	$847.98		$942.8702	$942.87	$942.85	$942.90