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	$58.66	13.312%	$66.4688	$66.47	$66.45	$66.50
Purchase #2	$200.80	7.859%	$216.5809	$216.58	$216.60	$216.60
Purchase #3	$180.33	7.610%	$194.0531	$194.05	$194.05	$194.10
Purchase #4	$99.37	8.862%	$108.1762	$108.18	$108.20	$108.20
Purchase #5	$165.71	10.367%	$182.8892	$182.89	$182.90	$182.90
Purchase #6	$57.89	4.817%	$60.6786	$60.68	$60.70	$60.70
Purchase #7	$166.84	3.628%	$172.893	$172.89	$172.90	$172.90
7 purchase totals =	$929.60		$1,001.7398	$1,001.74	$1,001.80	$1,001.90