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	$37.68	3.868%	$39.1375	$39.14	$39.15	$39.10
Purchase #2	$34.48	3.557%	$35.7065	$35.71	$35.70	$35.70
Purchase #3	$87.85	4.282%	$91.6117	$91.61	$91.60	$91.60
Purchase #4	$84.32	5.763%	$89.1794	$89.18	$89.20	$89.20
Purchase #5	$90.32	4.590%	$94.4657	$94.47	$94.45	$94.50
Purchase #6	$109.65	12.456%	$123.308	$123.31	$123.30	$123.30
Purchase #7	$25.41	12.133%	$28.493	$28.49	$28.50	$28.50
7 purchase totals =	$469.71		$501.9018	$501.91	$501.90	$501.90