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	$22.50	9.498%	$24.6371	$24.64	$24.65	$24.60
Purchase #2	$238.82	11.707%	$266.7787	$266.78	$266.80	$266.80
Purchase #3	$142.37	4.300%	$148.4919	$148.49	$148.50	$148.50
Purchase #4	$77.49	6.687%	$82.6718	$82.67	$82.65	$82.70
Purchase #5	$153.78	9.862%	$168.9458	$168.95	$168.95	$168.90
Purchase #6	$18.80	13.778%	$21.3903	$21.39	$21.40	$21.40
Purchase #7	$131.93	9.566%	$144.5504	$144.55	$144.55	$144.60
7 purchase totals =	$785.69		$857.4660	$857.47	$857.50	$857.50