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	$110.59	11.688%	$123.5158	$123.52	$123.50	$123.50
Purchase #2	$92.57	7.511%	$99.5229	$99.52	$99.50	$99.50
Purchase #3	$76.63	11.639%	$85.549	$85.55	$85.55	$85.50
Purchase #4	$169.97	8.707%	$184.7693	$184.77	$184.75	$184.80
Purchase #5	$21.81	13.325%	$24.7162	$24.72	$24.70	$24.70
Purchase #6	$220.42	10.511%	$243.5883	$243.59	$243.60	$243.60
Purchase #7	$225.41	13.340%	$255.4797	$255.48	$255.50	$255.50
7 purchase totals =	$917.40		$1,017.1412	$1,017.15	$1,017.10	$1,017.10