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	$38.31	11.105%	$42.5643	$42.56	$42.55	$42.60
Purchase #2	$218.95	12.142%	$245.5349	$245.53	$245.55	$245.50
Purchase #3	$113.52	11.303%	$126.3512	$126.35	$126.35	$126.40
Purchase #4	$146.27	11.131%	$162.5513	$162.55	$162.55	$162.60
Purchase #5	$32.48	8.604%	$35.2746	$35.27	$35.25	$35.30
Purchase #6	$101.67	5.162%	$106.9182	$106.92	$106.90	$106.90
Purchase #7	$242.38	5.325%	$255.2867	$255.29	$255.30	$255.30
7 purchase totals =	$893.58		$974.4812	$974.47	$974.45	$974.60