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	$64.33	11.564%	$71.7691	$71.77	$71.75	$71.80
Purchase #2	$135.89	13.204%	$153.8329	$153.83	$153.85	$153.80
Purchase #3	$97.51	6.291%	$103.6444	$103.64	$103.65	$103.60
Purchase #4	$62.26	8.299%	$67.427	$67.43	$67.45	$67.40
Purchase #5	$69.35	9.763%	$76.1206	$76.12	$76.10	$76.10
Purchase #6	$125.40	13.869%	$142.7917	$142.79	$142.80	$142.80
Purchase #7	$38.53	10.430%	$42.5487	$42.55	$42.55	$42.50
7 purchase totals =	$593.27		$658.1344	$658.13	$658.15	$658.00