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	$229.92	9.133%	$250.9186	$250.92	$250.90	$250.90
Purchase #2	$54.34	5.430%	$57.2907	$57.29	$57.30	$57.30
Purchase #3	$21.94	9.802%	$24.0906	$24.09	$24.10	$24.10
Purchase #4	$49.87	12.745%	$56.2259	$56.23	$56.25	$56.20
Purchase #5	$169.61	13.357%	$192.2648	$192.26	$192.25	$192.30
Purchase #6	$113.51	8.816%	$123.517	$123.52	$123.50	$123.50
Purchase #7	$149.84	9.620%	$164.2546	$164.25	$164.25	$164.30
7 purchase totals =	$789.03		$868.5622	$868.56	$868.55	$868.60