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	$230.83	10.402%	$254.8409	$254.84	$254.85	$254.80
Purchase #2	$40.82	3.221%	$42.1348	$42.13	$42.15	$42.10
Purchase #3	$206.61	8.425%	$224.0169	$224.02	$224.00	$224.00
Purchase #4	$100.43	13.757%	$114.2462	$114.25	$114.25	$114.20
Purchase #5	$80.79	9.365%	$88.356	$88.36	$88.35	$88.40
Purchase #6	$71.92	9.314%	$78.6186	$78.62	$78.60	$78.60
Purchase #7	$95.29	11.771%	$106.5066	$106.51	$106.50	$106.50
7 purchase totals =	$826.69		$908.7200	$908.73	$908.70	$908.60