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	$72.34	12.848%	$81.6342	$81.63	$81.65	$81.60
Purchase #2	$35.76	4.534%	$37.3814	$37.38	$37.40	$37.40
Purchase #3	$109.51	9.817%	$120.2606	$120.26	$120.25	$120.30
Purchase #4	$18.89	7.619%	$20.3292	$20.33	$20.35	$20.30
Purchase #5	$196.39	6.388%	$208.9354	$208.94	$208.95	$208.90
Purchase #6	$172.86	13.461%	$196.1287	$196.13	$196.15	$196.10
Purchase #7	$130.53	6.516%	$139.0353	$139.04	$139.05	$139.00
7 purchase totals =	$736.28		$803.7048	$803.71	$803.80	$803.60