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	$92.47	6.810%	$98.7672	$98.77	$98.75	$98.80
Purchase #2	$124.72	4.146%	$129.8909	$129.89	$129.90	$129.90
Purchase #3	$117.79	8.269%	$127.5301	$127.53	$127.55	$127.50
Purchase #4	$22.73	9.395%	$24.8655	$24.87	$24.85	$24.90
Purchase #5	$198.56	6.660%	$211.7841	$211.78	$211.80	$211.80
Purchase #6	$7.34	6.411%	$7.8106	$7.81	$7.80	$7.80
Purchase #7	$60.76	6.750%	$64.8613	$64.86	$64.85	$64.90
7 purchase totals =	$624.37		$665.5097	$665.51	$665.50	$665.60