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	$150.39	5.833%	$159.1622	$159.16	$159.15	$159.20
Purchase #2	$141.74	7.744%	$152.7163	$152.72	$152.70	$152.70
Purchase #3	$177.97	7.253%	$190.8782	$190.88	$190.90	$190.90
Purchase #4	$108.93	6.392%	$115.8928	$115.89	$115.90	$115.90
Purchase #5	$155.68	8.484%	$168.8879	$168.89	$168.90	$168.90
Purchase #6	$31.37	12.480%	$35.285	$35.29	$35.30	$35.30
Purchase #7	$93.96	9.182%	$102.5874	$102.59	$102.60	$102.60
7 purchase totals =	$860.04		$925.4098	$925.42	$925.45	$925.50