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	$123.48	6.429%	$131.4185	$131.42	$131.40	$131.40
Purchase #2	$29.40	8.358%	$31.8573	$31.86	$31.85	$31.90
Purchase #3	$238.38	4.787%	$249.7913	$249.79	$249.80	$249.80
Purchase #4	$214.90	10.645%	$237.7761	$237.78	$237.80	$237.80
Purchase #5	$118.95	7.136%	$127.4383	$127.44	$127.45	$127.40
Purchase #6	$80.25	10.615%	$88.7685	$88.77	$88.75	$88.80
Purchase #7	$45.98	6.120%	$48.794	$48.79	$48.80	$48.80
7 purchase totals =	$851.34		$915.8440	$915.85	$915.85	$915.90