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	$31.31	12.599%	$35.2547	$35.25	$35.25	$35.30
Purchase #2	$59.54	10.276%	$65.6583	$65.66	$65.65	$65.70
Purchase #3	$203.77	7.206%	$218.4537	$218.45	$218.45	$218.50
Purchase #4	$235.31	13.302%	$266.6109	$266.61	$266.60	$266.60
Purchase #5	$91.36	11.342%	$101.7221	$101.72	$101.70	$101.70
Purchase #6	$170.76	5.569%	$180.2696	$180.27	$180.25	$180.30
Purchase #7	$23.89	4.214%	$24.8967	$24.90	$24.90	$24.90
7 purchase totals =	$815.94		$892.8660	$892.86	$892.80	$893.00