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	$109.89	6.487%	$117.0186	$117.02	$117.00	$117.00
Purchase #2	$38.72	10.778%	$42.8932	$42.89	$42.90	$42.90
Purchase #3	$57.78	13.251%	$65.4364	$65.44	$65.45	$65.40
Purchase #4	$31.77	12.247%	$35.6609	$35.66	$35.65	$35.70
Purchase #5	$52.99	11.745%	$59.2137	$59.21	$59.20	$59.20
Purchase #6	$84.89	9.429%	$92.8943	$92.89	$92.90	$92.90
Purchase #7	$144.60	11.660%	$161.4604	$161.46	$161.45	$161.50
7 purchase totals =	$520.64		$574.5775	$574.57	$574.55	$574.60