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	$79.84	3.529%	$82.6576	$82.66	$82.65	$82.70
Purchase #2	$72.96	5.443%	$76.9312	$76.93	$76.95	$76.90
Purchase #3	$205.30	5.617%	$216.8317	$216.83	$216.85	$216.80
Purchase #4	$35.37	12.799%	$39.897	$39.90	$39.90	$39.90
Purchase #5	$57.81	3.514%	$59.8414	$59.84	$59.85	$59.80
Purchase #6	$21.67	8.759%	$23.5681	$23.57	$23.55	$23.60
Purchase #7	$239.51	13.719%	$272.3684	$272.37	$272.35	$272.40
7 purchase totals =	$712.46		$772.0954	$772.10	$772.10	$772.10