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	$39.59	8.147%	$42.8154	$42.82	$42.80	$42.80
Purchase #2	$39.48	7.604%	$42.4821	$42.48	$42.50	$42.50
Purchase #3	$160.33	6.423%	$170.628	$170.63	$170.65	$170.60
Purchase #4	$77.55	5.423%	$81.7555	$81.76	$81.75	$81.80
Purchase #5	$56.41	3.143%	$58.183	$58.18	$58.20	$58.20
Purchase #6	$34.89	7.544%	$37.5221	$37.52	$37.50	$37.50
Purchase #7	$10.61	5.155%	$11.1569	$11.16	$11.15	$11.20
7 purchase totals =	$418.86		$444.5430	$444.55	$444.55	$444.60