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	$248.87	10.196%	$274.2448	$274.24	$274.25	$274.20
Purchase #2	$215.37	6.405%	$229.1644	$229.16	$229.15	$229.20
Purchase #3	$34.31	13.160%	$38.8252	$38.83	$38.85	$38.80
Purchase #4	$40.73	4.662%	$42.6288	$42.63	$42.65	$42.60
Purchase #5	$76.77	4.455%	$80.1901	$80.19	$80.20	$80.20
Purchase #6	$37.84	12.556%	$42.5912	$42.59	$42.60	$42.60
Purchase #7	$30.98	13.150%	$35.0539	$35.05	$35.05	$35.10
7 purchase totals =	$684.87		$742.6984	$742.69	$742.75	$742.70