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	$81.94	8.660%	$89.036	$89.04	$89.05	$89.00
Purchase #2	$85.61	11.166%	$95.1692	$95.17	$95.15	$95.20
Purchase #3	$98.59	4.868%	$103.3894	$103.39	$103.40	$103.40
Purchase #4	$35.81	8.706%	$38.9276	$38.93	$38.95	$38.90
Purchase #5	$93.39	10.529%	$103.223	$103.22	$103.20	$103.20
Purchase #6	$10.85	4.421%	$11.3297	$11.33	$11.35	$11.30
Purchase #7	$95.78	3.200%	$98.845	$98.85	$98.85	$98.80
7 purchase totals =	$501.97		$539.9199	$539.93	$539.95	$539.80