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	$38.42	10.772%	$42.5586	$42.56	$42.55	$42.60
Purchase #2	$27.28	13.575%	$30.9833	$30.98	$31.00	$31.00
Purchase #3	$36.77	10.507%	$40.6334	$40.63	$40.65	$40.60
Purchase #4	$203.63	4.531%	$212.8565	$212.86	$212.85	$212.90
Purchase #5	$189.64	3.621%	$196.5069	$196.51	$196.50	$196.50
Purchase #6	$46.58	4.377%	$48.6188	$48.62	$48.60	$48.60
Purchase #7	$34.25	8.329%	$37.1027	$37.10	$37.10	$37.10
7 purchase totals =	$576.57		$609.2602	$609.26	$609.25	$609.30