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	$31.29	6.832%	$33.4277	$33.43	$33.45	$33.40
Purchase #2	$48.77	4.266%	$50.8505	$50.85	$50.85	$50.90
Purchase #3	$99.52	12.867%	$112.3252	$112.33	$112.35	$112.30
Purchase #4	$226.99	12.734%	$255.8949	$255.89	$255.90	$255.90
Purchase #5	$22.51	3.658%	$23.3334	$23.33	$23.35	$23.30
Purchase #6	$184.68	13.521%	$209.6506	$209.65	$209.65	$209.70
Purchase #7	$86.83	13.543%	$98.5894	$98.59	$98.60	$98.60
7 purchase totals =	$700.59		$784.0717	$784.07	$784.15	$784.10