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	$111.92	11.195%	$124.4494	$124.45	$124.45	$124.40
Purchase #2	$48.73	9.213%	$53.2195	$53.22	$53.20	$53.20
Purchase #3	$102.32	11.361%	$113.9446	$113.94	$113.95	$113.90
Purchase #4	$41.97	4.573%	$43.8893	$43.89	$43.90	$43.90
Purchase #5	$131.81	12.718%	$148.5736	$148.57	$148.55	$148.60
Purchase #6	$40.60	10.738%	$44.9596	$44.96	$44.95	$45.00
Purchase #7	$11.72	6.249%	$12.4524	$12.45	$12.45	$12.50
7 purchase totals =	$489.07		$541.4884	$541.48	$541.45	$541.50