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	$110.53	8.402%	$119.8167	$119.82	$119.80	$119.80
Purchase #2	$54.39	13.475%	$61.7191	$61.72	$61.70	$61.70
Purchase #3	$16.89	9.123%	$18.4309	$18.43	$18.45	$18.40
Purchase #4	$193.34	5.482%	$203.9389	$203.94	$203.95	$203.90
Purchase #5	$238.38	11.539%	$265.8867	$265.89	$265.90	$265.90
Purchase #6	$126.42	10.329%	$139.4779	$139.48	$139.50	$139.50
Purchase #7	$24.71	3.562%	$25.5902	$25.59	$25.60	$25.60
7 purchase totals =	$764.66		$834.8604	$834.87	$834.90	$834.80