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	$75.93	7.616%	$81.7128	$81.71	$81.70	$81.70
Purchase #2	$98.81	10.746%	$109.4281	$109.43	$109.45	$109.40
Purchase #3	$67.85	8.523%	$73.6329	$73.63	$73.65	$73.60
Purchase #4	$81.39	11.717%	$90.9265	$90.93	$90.95	$90.90
Purchase #5	$92.82	13.198%	$105.0704	$105.07	$105.05	$105.10
Purchase #6	$53.95	13.202%	$61.0725	$61.07	$61.05	$61.10
Purchase #7	$5.40	9.659%	$5.9216	$5.92	$5.90	$5.90
7 purchase totals =	$476.15		$527.7648	$527.76	$527.75	$527.70