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	$93.85	5.735%	$99.2323	$99.23	$99.25	$99.20
Purchase #2	$135.32	5.342%	$142.5488	$142.55	$142.55	$142.50
Purchase #3	$123.47	10.182%	$136.0417	$136.04	$136.05	$136.00
Purchase #4	$221.89	11.226%	$246.7994	$246.80	$246.80	$246.80
Purchase #5	$196.90	6.594%	$209.8836	$209.88	$209.90	$209.90
Purchase #6	$248.92	13.128%	$281.5982	$281.60	$281.60	$281.60
Purchase #7	$138.36	8.703%	$150.4015	$150.40	$150.40	$150.40
7 purchase totals =	$1,158.71		$1,266.5055	$1,266.50	$1,266.55	$1,266.40