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	$136.90	7.144%	$146.6801	$146.68	$146.70	$146.70
Purchase #2	$78.38	6.139%	$83.1917	$83.19	$83.20	$83.20
Purchase #3	$53.42	11.866%	$59.7588	$59.76	$59.75	$59.80
Purchase #4	$76.34	11.292%	$84.9603	$84.96	$84.95	$85.00
Purchase #5	$139.75	3.828%	$145.0996	$145.10	$145.10	$145.10
Purchase #6	$216.78	10.216%	$238.9262	$238.93	$238.95	$238.90
Purchase #7	$65.75	11.380%	$73.2324	$73.23	$73.25	$73.20
7 purchase totals =	$767.32		$831.8491	$831.85	$831.90	$831.90