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	$60.40	9.556%	$66.1718	$66.17	$66.15	$66.20
Purchase #2	$38.88	11.564%	$43.3761	$43.38	$43.40	$43.40
Purchase #3	$238.43	3.517%	$246.8156	$246.82	$246.80	$246.80
Purchase #4	$191.55	12.865%	$216.1929	$216.19	$216.20	$216.20
Purchase #5	$231.90	10.171%	$255.4865	$255.49	$255.50	$255.50
Purchase #6	$222.60	3.864%	$231.2013	$231.20	$231.20	$231.20
Purchase #7	$37.73	10.270%	$41.6049	$41.60	$41.60	$41.60
7 purchase totals =	$1,021.49		$1,100.8491	$1,100.85	$1,100.85	$1,100.90