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	$229.90	12.254%	$258.0719	$258.07	$258.05	$258.10
Purchase #2	$137.80	6.516%	$146.779	$146.78	$146.80	$146.80
Purchase #3	$35.93	13.262%	$40.695	$40.70	$40.70	$40.70
Purchase #4	$90.88	9.313%	$99.3437	$99.34	$99.35	$99.30
Purchase #5	$216.94	4.763%	$227.2729	$227.27	$227.25	$227.30
Purchase #6	$117.87	12.494%	$132.5967	$132.60	$132.60	$132.60
Purchase #7	$67.54	6.483%	$71.9186	$71.92	$71.90	$71.90
7 purchase totals =	$896.86		$976.6778	$976.68	$976.65	$976.70