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	$78.42	7.750%	$84.4976	$84.50	$84.50	$84.50
Purchase #2	$54.50	8.806%	$59.2993	$59.30	$59.30	$59.30
Purchase #3	$151.87	13.760%	$172.7673	$172.77	$172.75	$172.80
Purchase #4	$204.33	5.451%	$215.468	$215.47	$215.45	$215.50
Purchase #5	$112.97	3.545%	$116.9748	$116.97	$116.95	$117.00
Purchase #6	$160.58	5.533%	$169.4649	$169.46	$169.45	$169.50
Purchase #7	$30.90	5.585%	$32.6258	$32.63	$32.65	$32.60
7 purchase totals =	$793.57		$851.0977	$851.10	$851.05	$851.20