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	$241.27	9.662%	$264.5815	$264.58	$264.60	$264.60
Purchase #2	$69.39	12.238%	$77.8819	$77.88	$77.90	$77.90
Purchase #3	$148.54	7.448%	$159.6033	$159.60	$159.60	$159.60
Purchase #4	$246.90	3.180%	$254.7514	$254.75	$254.75	$254.80
Purchase #5	$137.38	9.369%	$150.2511	$150.25	$150.25	$150.30
Purchase #6	$53.35	4.306%	$55.6473	$55.65	$55.65	$55.60
Purchase #7	$28.34	5.339%	$29.8531	$29.85	$29.85	$29.90
7 purchase totals =	$925.17		$992.5696	$992.56	$992.60	$992.70