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	$40.69	12.334%	$45.7087	$45.71	$45.70	$45.70
Purchase #2	$45.89	5.357%	$48.3483	$48.35	$48.35	$48.30
Purchase #3	$181.34	9.685%	$198.9028	$198.90	$198.90	$198.90
Purchase #4	$32.62	8.578%	$35.4181	$35.42	$35.40	$35.40
Purchase #5	$205.89	6.113%	$218.4761	$218.48	$218.50	$218.50
Purchase #6	$220.50	10.131%	$242.8389	$242.84	$242.85	$242.80
Purchase #7	$120.88	9.145%	$131.9345	$131.93	$131.95	$131.90
7 purchase totals =	$847.81		$921.6274	$921.63	$921.65	$921.50