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	$37.57	4.800%	$39.3734	$39.37	$39.35	$39.40
Purchase #2	$35.52	13.141%	$40.1877	$40.19	$40.20	$40.20
Purchase #3	$53.88	4.823%	$56.4786	$56.48	$56.50	$56.50
Purchase #4	$146.68	6.170%	$155.7302	$155.73	$155.75	$155.70
Purchase #5	$76.26	9.461%	$83.475	$83.48	$83.50	$83.50
Purchase #6	$31.89	3.698%	$33.0693	$33.07	$33.05	$33.10
Purchase #7	$171.42	11.167%	$190.5625	$190.56	$190.55	$190.60
7 purchase totals =	$553.22		$598.8767	$598.88	$598.90	$599.00