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	$240.54	9.266%	$262.8284	$262.83	$262.85	$262.80
Purchase #2	$178.62	10.155%	$196.7589	$196.76	$196.75	$196.80
Purchase #3	$22.86	12.267%	$25.6642	$25.66	$25.65	$25.70
Purchase #4	$73.69	8.527%	$79.9735	$79.97	$79.95	$80.00
Purchase #5	$82.46	5.407%	$86.9186	$86.92	$86.90	$86.90
Purchase #6	$81.64	13.329%	$92.5218	$92.52	$92.50	$92.50
Purchase #7	$41.92	9.567%	$45.9305	$45.93	$45.95	$45.90
7 purchase totals =	$721.73		$790.5959	$790.59	$790.55	$790.60