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	$224.34	7.151%	$240.3826	$240.38	$240.40	$240.40
Purchase #2	$104.25	11.561%	$116.3023	$116.30	$116.30	$116.30
Purchase #3	$223.84	11.721%	$250.0763	$250.08	$250.10	$250.10
Purchase #4	$92.57	13.564%	$105.1262	$105.13	$105.15	$105.10
Purchase #5	$91.84	12.791%	$103.5873	$103.59	$103.60	$103.60
Purchase #6	$85.64	3.325%	$88.4875	$88.49	$88.50	$88.50
Purchase #7	$40.39	4.499%	$42.2071	$42.21	$42.20	$42.20
7 purchase totals =	$862.87		$946.1693	$946.18	$946.25	$946.20