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	$15.80	4.597%	$16.5263	$16.53	$16.55	$16.50
Purchase #2	$65.90	4.525%	$68.882	$68.88	$68.90	$68.90
Purchase #3	$188.43	6.342%	$200.3802	$200.38	$200.40	$200.40
Purchase #4	$179.99	11.334%	$200.3901	$200.39	$200.40	$200.40
Purchase #5	$86.63	3.222%	$89.4212	$89.42	$89.40	$89.40
Purchase #6	$191.75	8.676%	$208.3862	$208.39	$208.40	$208.40
Purchase #7	$105.53	13.741%	$120.0309	$120.03	$120.05	$120.00
7 purchase totals =	$834.03		$904.0169	$904.02	$904.10	$904.00