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	$126.94	7.815%	$136.8604	$136.86	$136.85	$136.90
Purchase #2	$238.47	4.796%	$249.907	$249.91	$249.90	$249.90
Purchase #3	$58.69	13.185%	$66.4283	$66.43	$66.45	$66.40
Purchase #4	$50.78	12.126%	$56.9376	$56.94	$56.95	$56.90
Purchase #5	$115.66	4.120%	$120.4252	$120.43	$120.45	$120.40
Purchase #6	$139.48	3.514%	$144.3813	$144.38	$144.40	$144.40
Purchase #7	$44.42	13.539%	$50.434	$50.43	$50.45	$50.40
7 purchase totals =	$774.44		$825.3738	$825.38	$825.45	$825.30