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	$224.51	7.154%	$240.5714	$240.57	$240.55	$240.60
Purchase #2	$38.70	11.113%	$43.0007	$43.00	$43.00	$43.00
Purchase #3	$139.31	8.373%	$150.9744	$150.97	$150.95	$151.00
Purchase #4	$81.92	10.463%	$90.4913	$90.49	$90.50	$90.50
Purchase #5	$23.72	4.576%	$24.8054	$24.81	$24.80	$24.80
Purchase #6	$65.42	10.695%	$72.4167	$72.42	$72.40	$72.40
Purchase #7	$26.29	3.510%	$27.2128	$27.21	$27.20	$27.20
7 purchase totals =	$599.87		$649.4727	$649.47	$649.40	$649.50