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	$106.71	13.268%	$120.8683	$120.87	$120.85	$120.90
Purchase #2	$53.35	4.850%	$55.9375	$55.94	$55.95	$55.90
Purchase #3	$147.42	6.725%	$157.334	$157.33	$157.35	$157.30
Purchase #4	$81.86	9.673%	$89.7783	$89.78	$89.80	$89.80
Purchase #5	$122.52	6.691%	$130.7178	$130.72	$130.70	$130.70
Purchase #6	$63.69	5.105%	$66.9414	$66.94	$66.95	$66.90
Purchase #7	$195.98	6.578%	$208.8716	$208.87	$208.85	$208.90
7 purchase totals =	$771.53		$830.4489	$830.45	$830.45	$830.40