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	$75.45	5.189%	$79.3651	$79.37	$79.35	$79.40
Purchase #2	$147.41	10.184%	$162.4222	$162.42	$162.40	$162.40
Purchase #3	$150.80	5.368%	$158.8949	$158.89	$158.90	$158.90
Purchase #4	$77.75	12.768%	$87.6771	$87.68	$87.70	$87.70
Purchase #5	$55.34	11.689%	$61.8087	$61.81	$61.80	$61.80
Purchase #6	$171.78	11.356%	$191.2873	$191.29	$191.30	$191.30
Purchase #7	$217.53	9.413%	$238.0061	$238.01	$238.00	$238.00
7 purchase totals =	$896.06		$979.4614	$979.47	$979.45	$979.50