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	$65.66	9.316%	$71.7769	$71.78	$71.80	$71.80
Purchase #2	$136.50	10.412%	$150.7124	$150.71	$150.70	$150.70
Purchase #3	$95.54	9.800%	$104.9029	$104.90	$104.90	$104.90
Purchase #4	$24.83	8.160%	$26.8561	$26.86	$26.85	$26.90
Purchase #5	$126.54	12.122%	$141.8792	$141.88	$141.90	$141.90
Purchase #6	$90.84	3.507%	$94.0258	$94.03	$94.05	$94.00
Purchase #7	$59.39	12.580%	$66.8613	$66.86	$66.85	$66.90
7 purchase totals =	$599.30		$657.0146	$657.02	$657.05	$657.10