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	$72.32	8.652%	$78.5771	$78.58	$78.60	$78.60
Purchase #2	$82.78	11.578%	$92.3643	$92.36	$92.35	$92.40
Purchase #3	$98.47	11.421%	$109.7163	$109.72	$109.70	$109.70
Purchase #4	$54.60	9.122%	$59.5806	$59.58	$59.60	$59.60
Purchase #5	$113.35	9.379%	$123.9811	$123.98	$124.00	$124.00
Purchase #6	$30.88	11.642%	$34.475	$34.48	$34.50	$34.50
Purchase #7	$13.74	8.325%	$14.8839	$14.88	$14.90	$14.90
7 purchase totals =	$466.14		$513.5783	$513.58	$513.65	$513.70