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	$249.82	11.342%	$278.1546	$278.15	$278.15	$278.20
Purchase #2	$134.95	3.459%	$139.6179	$139.62	$139.60	$139.60
Purchase #3	$198.33	12.544%	$223.2085	$223.21	$223.20	$223.20
Purchase #4	$117.81	3.189%	$121.567	$121.57	$121.55	$121.60
Purchase #5	$55.71	8.380%	$60.3785	$60.38	$60.40	$60.40
Purchase #6	$112.71	3.119%	$116.2254	$116.23	$116.25	$116.20
Purchase #7	$73.53	13.704%	$83.6066	$83.61	$83.60	$83.60
7 purchase totals =	$942.86		$1,022.7585	$1,022.77	$1,022.75	$1,022.80