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	$48.96	3.220%	$50.5365	$50.54	$50.55	$50.50
Purchase #2	$123.27	5.637%	$130.2187	$130.22	$130.20	$130.20
Purchase #3	$56.81	6.584%	$60.5504	$60.55	$60.55	$60.60
Purchase #4	$139.30	7.686%	$150.0066	$150.01	$150.00	$150.00
Purchase #5	$78.49	9.475%	$85.9269	$85.93	$85.95	$85.90
Purchase #6	$141.70	7.688%	$152.5939	$152.59	$152.60	$152.60
Purchase #7	$120.57	8.862%	$131.2549	$131.25	$131.25	$131.30
7 purchase totals =	$709.10		$761.0879	$761.09	$761.10	$761.10