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	$38.73	11.671%	$43.2502	$43.25	$43.25	$43.30
Purchase #2	$165.90	4.229%	$172.9159	$172.92	$172.90	$172.90
Purchase #3	$96.47	6.221%	$102.4714	$102.47	$102.45	$102.50
Purchase #4	$152.63	10.339%	$168.4104	$168.41	$168.40	$168.40
Purchase #5	$88.32	13.799%	$100.5073	$100.51	$100.50	$100.50
Purchase #6	$215.37	12.112%	$241.4556	$241.46	$241.45	$241.50
Purchase #7	$34.34	5.224%	$36.1339	$36.13	$36.15	$36.10
7 purchase totals =	$791.76		$865.1447	$865.15	$865.10	$865.20