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	$227.73	12.706%	$256.6654	$256.67	$256.65	$256.70
Purchase #2	$41.89	3.387%	$43.3088	$43.31	$43.30	$43.30
Purchase #3	$35.72	5.411%	$37.6528	$37.65	$37.65	$37.70
Purchase #4	$138.55	7.725%	$149.253	$149.25	$149.25	$149.30
Purchase #5	$142.97	12.761%	$161.2144	$161.21	$161.20	$161.20
Purchase #6	$136.29	10.740%	$150.9275	$150.93	$150.95	$150.90
Purchase #7	$6.68	12.425%	$7.51	$7.51	$7.50	$7.50
7 purchase totals =	$729.83		$806.5319	$806.53	$806.50	$806.60