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	$121.48	12.339%	$136.4694	$136.47	$136.45	$136.50
Purchase #2	$12.37	4.507%	$12.9275	$12.93	$12.95	$12.90
Purchase #3	$112.78	7.503%	$121.2419	$121.24	$121.25	$121.20
Purchase #4	$123.31	13.191%	$139.5758	$139.58	$139.60	$139.60
Purchase #5	$108.93	8.442%	$118.1259	$118.13	$118.15	$118.10
Purchase #6	$131.54	6.656%	$140.2953	$140.30	$140.30	$140.30
Purchase #7	$74.48	11.309%	$82.9029	$82.90	$82.90	$82.90
7 purchase totals =	$684.89		$751.5387	$751.55	$751.60	$751.50