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	$31.53	13.285%	$35.7188	$35.72	$35.70	$35.70
Purchase #2	$84.77	8.766%	$92.2009	$92.20	$92.20	$92.20
Purchase #3	$201.46	7.651%	$216.8737	$216.87	$216.85	$216.90
Purchase #4	$83.41	8.378%	$90.3981	$90.40	$90.40	$90.40
Purchase #5	$26.89	3.307%	$27.7793	$27.78	$27.80	$27.80
Purchase #6	$35.26	8.831%	$38.3738	$38.37	$38.35	$38.40
Purchase #7	$32.72	8.561%	$35.5212	$35.52	$35.50	$35.50
7 purchase totals =	$496.04		$536.8658	$536.86	$536.80	$536.90