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	$37.89	12.111%	$42.4789	$42.48	$42.50	$42.50
Purchase #2	$35.32	7.513%	$37.9736	$37.97	$37.95	$38.00
Purchase #3	$167.90	4.549%	$175.5378	$175.54	$175.55	$175.50
Purchase #4	$87.79	7.757%	$94.5999	$94.60	$94.60	$94.60
Purchase #5	$34.38	8.225%	$37.2078	$37.21	$37.20	$37.20
Purchase #6	$172.98	11.169%	$192.3001	$192.30	$192.30	$192.30
Purchase #7	$80.53	13.304%	$91.2437	$91.24	$91.25	$91.20
7 purchase totals =	$616.79		$671.3418	$671.34	$671.35	$671.30