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	$109.91	12.278%	$123.4047	$123.40	$123.40	$123.40
Purchase #2	$130.64	11.267%	$145.3592	$145.36	$145.35	$145.40
Purchase #3	$246.96	11.308%	$274.8862	$274.89	$274.90	$274.90
Purchase #4	$238.96	4.439%	$249.5674	$249.57	$249.55	$249.60
Purchase #5	$193.98	6.159%	$205.9272	$205.93	$205.95	$205.90
Purchase #6	$12.54	4.720%	$13.1319	$13.13	$13.15	$13.10
Purchase #7	$86.38	8.108%	$93.3837	$93.38	$93.40	$93.40
7 purchase totals =	$1,019.37		$1,105.6603	$1,105.66	$1,105.70	$1,105.70