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	$99.37	6.792%	$106.1192	$106.12	$106.10	$106.10
Purchase #2	$139.99	7.583%	$150.6054	$150.61	$150.60	$150.60
Purchase #3	$36.92	5.354%	$38.8967	$38.90	$38.90	$38.90
Purchase #4	$193.67	11.793%	$216.5095	$216.51	$216.50	$216.50
Purchase #5	$66.53	7.641%	$71.6136	$71.61	$71.60	$71.60
Purchase #6	$59.57	11.381%	$66.3497	$66.35	$66.35	$66.30
Purchase #7	$142.45	7.361%	$152.9357	$152.94	$152.95	$152.90
7 purchase totals =	$738.50		$803.0298	$803.04	$803.00	$802.90