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	$29.69	13.852%	$33.8027	$33.80	$33.80	$33.80
Purchase #2	$194.39	9.166%	$212.2078	$212.21	$212.20	$212.20
Purchase #3	$32.54	9.324%	$35.574	$35.57	$35.55	$35.60
Purchase #4	$87.82	3.372%	$90.7813	$90.78	$90.80	$90.80
Purchase #5	$77.76	13.216%	$88.0368	$88.04	$88.05	$88.00
Purchase #6	$234.64	9.676%	$257.3438	$257.34	$257.35	$257.30
Purchase #7	$138.77	9.238%	$151.5896	$151.59	$151.60	$151.60
7 purchase totals =	$795.61		$869.3360	$869.33	$869.35	$869.30