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	$108.79	6.306%	$115.6503	$115.65	$115.65	$115.70
Purchase #2	$120.47	9.389%	$131.7809	$131.78	$131.80	$131.80
Purchase #3	$61.36	4.447%	$64.0887	$64.09	$64.10	$64.10
Purchase #4	$34.65	8.538%	$37.6084	$37.61	$37.60	$37.60
Purchase #5	$250.39	9.774%	$274.8631	$274.86	$274.85	$274.90
Purchase #6	$75.36	10.650%	$83.3858	$83.39	$83.40	$83.40
Purchase #7	$101.54	11.346%	$113.0607	$113.06	$113.05	$113.10
7 purchase totals =	$752.56		$820.4379	$820.44	$820.45	$820.60