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	$67.68	7.261%	$72.5942	$72.59	$72.60	$72.60
Purchase #2	$38.62	4.128%	$40.2142	$40.21	$40.20	$40.20
Purchase #3	$218.92	9.467%	$239.6452	$239.65	$239.65	$239.60
Purchase #4	$18.51	9.780%	$20.3203	$20.32	$20.30	$20.30
Purchase #5	$172.78	4.321%	$180.2458	$180.25	$180.25	$180.20
Purchase #6	$219.88	3.517%	$227.6132	$227.61	$227.60	$227.60
Purchase #7	$143.59	5.334%	$151.2491	$151.25	$151.25	$151.20
7 purchase totals =	$879.98		$931.8820	$931.88	$931.85	$931.70