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	$102.82	9.635%	$112.7267	$112.73	$112.75	$112.70
Purchase #2	$24.95	11.799%	$27.8939	$27.89	$27.90	$27.90
Purchase #3	$140.95	5.306%	$148.4288	$148.43	$148.45	$148.40
Purchase #4	$168.98	12.440%	$190.0011	$190.00	$190.00	$190.00
Purchase #5	$112.75	3.680%	$116.8992	$116.90	$116.90	$116.90
Purchase #6	$88.68	12.204%	$99.5025	$99.50	$99.50	$99.50
Purchase #7	$134.72	12.390%	$151.4118	$151.41	$151.40	$151.40
7 purchase totals =	$773.85		$846.8640	$846.86	$846.90	$846.80