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	$34.94	13.328%	$39.5968	$39.60	$39.60	$39.60
Purchase #2	$72.43	11.526%	$80.7783	$80.78	$80.80	$80.80
Purchase #3	$235.39	3.741%	$244.1959	$244.20	$244.20	$244.20
Purchase #4	$46.93	3.575%	$48.6077	$48.61	$48.60	$48.60
Purchase #5	$227.93	6.599%	$242.9711	$242.97	$242.95	$243.00
Purchase #6	$161.59	13.213%	$182.9409	$182.94	$182.95	$182.90
Purchase #7	$211.63	5.282%	$222.8083	$222.81	$222.80	$222.80
7 purchase totals =	$990.84		$1,061.8990	$1,061.91	$1,061.90	$1,061.90