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	$42.90	10.736%	$47.5057	$47.51	$47.50	$47.50
Purchase #2	$55.36	8.358%	$59.987	$59.99	$60.00	$60.00
Purchase #3	$159.89	4.189%	$166.5878	$166.59	$166.60	$166.60
Purchase #4	$75.65	10.346%	$83.4767	$83.48	$83.50	$83.50
Purchase #5	$85.42	4.245%	$89.0461	$89.05	$89.05	$89.00
Purchase #6	$83.45	12.674%	$94.0265	$94.03	$94.05	$94.00
Purchase #7	$65.62	5.707%	$69.3649	$69.36	$69.35	$69.40
7 purchase totals =	$568.29		$609.9947	$610.01	$610.05	$610.00