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	$57.97	5.698%	$61.2731	$61.27	$61.25	$61.30
Purchase #2	$100.45	9.660%	$110.1535	$110.15	$110.15	$110.20
Purchase #3	$23.35	7.561%	$25.1155	$25.12	$25.10	$25.10
Purchase #4	$112.43	6.619%	$119.8717	$119.87	$119.85	$119.90
Purchase #5	$93.38	6.584%	$99.5281	$99.53	$99.55	$99.50
Purchase #6	$102.27	7.232%	$109.6662	$109.67	$109.65	$109.70
Purchase #7	$77.39	11.105%	$85.9842	$85.98	$86.00	$86.00
7 purchase totals =	$567.24		$611.5923	$611.59	$611.55	$611.70