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	$238.92	10.844%	$264.8285	$264.83	$264.85	$264.80
Purchase #2	$48.79	6.427%	$51.9257	$51.93	$51.95	$51.90
Purchase #3	$83.53	7.165%	$89.5149	$89.51	$89.50	$89.50
Purchase #4	$175.34	12.831%	$197.8379	$197.84	$197.85	$197.80
Purchase #5	$72.70	12.200%	$81.5694	$81.57	$81.55	$81.60
Purchase #6	$41.85	7.749%	$45.093	$45.09	$45.10	$45.10
Purchase #7	$50.68	5.291%	$53.3615	$53.36	$53.35	$53.40
7 purchase totals =	$711.81		$784.1309	$784.13	$784.15	$784.10