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	$63.73	4.341%	$66.4965	$66.50	$66.50	$66.50
Purchase #2	$59.33	3.303%	$61.2897	$61.29	$61.30	$61.30
Purchase #3	$81.80	8.107%	$88.4315	$88.43	$88.45	$88.40
Purchase #4	$54.72	11.808%	$61.1813	$61.18	$61.20	$61.20
Purchase #5	$172.72	7.512%	$185.6947	$185.69	$185.70	$185.70
Purchase #6	$217.63	11.217%	$242.0416	$242.04	$242.05	$242.00
Purchase #7	$197.26	13.409%	$223.7106	$223.71	$223.70	$223.70
7 purchase totals =	$847.19		$928.8459	$928.84	$928.90	$928.80