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	$84.41	7.187%	$90.4765	$90.48	$90.50	$90.50
Purchase #2	$125.94	8.422%	$136.5467	$136.55	$136.55	$136.50
Purchase #3	$137.35	9.230%	$150.0274	$150.03	$150.05	$150.00
Purchase #4	$106.28	5.842%	$112.4889	$112.49	$112.50	$112.50
Purchase #5	$161.50	11.244%	$179.6591	$179.66	$179.65	$179.70
Purchase #6	$55.73	9.546%	$61.05	$61.05	$61.05	$61.10
Purchase #7	$78.60	4.701%	$82.295	$82.30	$82.30	$82.30
7 purchase totals =	$749.81		$812.5436	$812.56	$812.60	$812.60