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	$122.53	7.130%	$131.2664	$131.27	$131.25	$131.30
Purchase #2	$87.39	4.802%	$91.5865	$91.59	$91.60	$91.60
Purchase #3	$152.26	8.683%	$165.4807	$165.48	$165.50	$165.50
Purchase #4	$71.72	7.642%	$77.2008	$77.20	$77.20	$77.20
Purchase #5	$37.42	7.676%	$40.2924	$40.29	$40.30	$40.30
Purchase #6	$206.77	4.816%	$216.728	$216.73	$216.75	$216.70
Purchase #7	$182.34	4.805%	$191.1014	$191.10	$191.10	$191.10
7 purchase totals =	$860.43		$913.6562	$913.66	$913.70	$913.70