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	$10.53	7.684%	$11.3391	$11.34	$11.35	$11.30
Purchase #2	$101.36	4.347%	$105.7661	$105.77	$105.75	$105.80
Purchase #3	$139.52	5.641%	$147.3903	$147.39	$147.40	$147.40
Purchase #4	$137.37	6.576%	$146.4035	$146.40	$146.40	$146.40
Purchase #5	$30.37	3.810%	$31.5271	$31.53	$31.55	$31.50
Purchase #6	$171.36	5.549%	$180.8688	$180.87	$180.85	$180.90
Purchase #7	$84.31	6.798%	$90.0414	$90.04	$90.05	$90.00
7 purchase totals =	$674.82		$713.3363	$713.34	$713.35	$713.30