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	$35.82	11.136%	$39.8089	$39.81	$39.80	$39.80
Purchase #2	$6.28	12.328%	$7.0542	$7.05	$7.05	$7.10
Purchase #3	$118.72	7.278%	$127.3604	$127.36	$127.35	$127.40
Purchase #4	$175.48	5.692%	$185.4683	$185.47	$185.45	$185.50
Purchase #5	$210.49	13.350%	$238.5904	$238.59	$238.60	$238.60
Purchase #6	$57.93	4.767%	$60.6915	$60.69	$60.70	$60.70
Purchase #7	$156.63	10.413%	$172.9399	$172.94	$172.95	$172.90
7 purchase totals =	$761.35		$831.9136	$831.91	$831.90	$832.00