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	$76.95	9.217%	$84.0425	$84.04	$84.05	$84.00
Purchase #2	$28.66	11.125%	$31.8484	$31.85	$31.85	$31.80
Purchase #3	$127.49	9.427%	$139.5085	$139.51	$139.50	$139.50
Purchase #4	$199.70	4.698%	$209.0819	$209.08	$209.10	$209.10
Purchase #5	$88.48	13.389%	$100.3266	$100.33	$100.35	$100.30
Purchase #6	$181.38	10.554%	$200.5228	$200.52	$200.50	$200.50
Purchase #7	$109.88	13.366%	$124.5666	$124.57	$124.55	$124.60
7 purchase totals =	$812.54		$889.8973	$889.90	$889.90	$889.80