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	$248.41	3.166%	$256.2747	$256.27	$256.25	$256.30
Purchase #2	$80.77	11.853%	$90.3437	$90.34	$90.35	$90.30
Purchase #3	$55.81	6.187%	$59.263	$59.26	$59.25	$59.30
Purchase #4	$117.35	7.131%	$125.7182	$125.72	$125.70	$125.70
Purchase #5	$100.89	4.140%	$105.0668	$105.07	$105.05	$105.10
Purchase #6	$46.55	6.559%	$49.6032	$49.60	$49.60	$49.60
Purchase #7	$180.61	7.332%	$193.8523	$193.85	$193.85	$193.90
7 purchase totals =	$830.39		$880.1219	$880.11	$880.05	$880.20