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	$20.81	3.754%	$21.5912	$21.59	$21.60	$21.60
Purchase #2	$208.29	7.771%	$224.4762	$224.48	$224.50	$224.50
Purchase #3	$240.25	4.303%	$250.588	$250.59	$250.60	$250.60
Purchase #4	$116.38	12.216%	$130.597	$130.60	$130.60	$130.60
Purchase #5	$238.49	10.614%	$263.8033	$263.80	$263.80	$263.80
Purchase #6	$96.79	5.392%	$102.0089	$102.01	$102.00	$102.00
Purchase #7	$132.61	4.685%	$138.8228	$138.82	$138.80	$138.80
7 purchase totals =	$1,053.62		$1,131.8874	$1,131.89	$1,131.90	$1,131.90