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	$122.99	11.480%	$137.1093	$137.11	$137.10	$137.10
Purchase #2	$90.56	5.170%	$95.242	$95.24	$95.25	$95.20
Purchase #3	$37.97	7.697%	$40.8926	$40.89	$40.90	$40.90
Purchase #4	$197.58	6.531%	$210.4839	$210.48	$210.50	$210.50
Purchase #5	$74.86	13.644%	$85.0739	$85.07	$85.05	$85.10
Purchase #6	$203.93	7.338%	$218.8944	$218.89	$218.90	$218.90
Purchase #7	$232.60	8.866%	$253.2223	$253.22	$253.20	$253.20
7 purchase totals =	$960.49		$1,040.9184	$1,040.90	$1,040.90	$1,040.90