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	$165.64	13.338%	$187.7331	$187.73	$187.75	$187.70
Purchase #2	$130.82	13.540%	$148.533	$148.53	$148.55	$148.50
Purchase #3	$60.70	8.665%	$65.9597	$65.96	$65.95	$66.00
Purchase #4	$112.87	9.211%	$123.2665	$123.27	$123.25	$123.30
Purchase #5	$113.45	11.271%	$126.2369	$126.24	$126.25	$126.20
Purchase #6	$36.52	10.234%	$40.2575	$40.26	$40.25	$40.30
Purchase #7	$55.66	3.122%	$57.3977	$57.40	$57.40	$57.40
7 purchase totals =	$675.66		$749.3844	$749.39	$749.40	$749.40