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	$45.50	3.381%	$47.0384	$47.04	$47.05	$47.00
Purchase #2	$44.74	7.169%	$47.9474	$47.95	$47.95	$47.90
Purchase #3	$128.82	6.427%	$137.0993	$137.10	$137.10	$137.10
Purchase #4	$126.95	10.693%	$140.5248	$140.52	$140.50	$140.50
Purchase #5	$10.76	7.276%	$11.5429	$11.54	$11.55	$11.50
Purchase #6	$71.49	12.766%	$80.6164	$80.62	$80.60	$80.60
Purchase #7	$29.81	13.728%	$33.9023	$33.90	$33.90	$33.90
7 purchase totals =	$458.07		$498.6715	$498.67	$498.65	$498.50