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	$35.43	7.269%	$38.0054	$38.01	$38.00	$38.00
Purchase #2	$81.71	11.177%	$90.8427	$90.84	$90.85	$90.80
Purchase #3	$76.53	3.799%	$79.4374	$79.44	$79.45	$79.40
Purchase #4	$183.96	9.210%	$200.9027	$200.90	$200.90	$200.90
Purchase #5	$56.30	10.306%	$62.1023	$62.10	$62.10	$62.10
Purchase #6	$39.77	4.237%	$41.4551	$41.46	$41.45	$41.50
Purchase #7	$38.40	7.762%	$41.3806	$41.38	$41.40	$41.40
7 purchase totals =	$512.10		$554.1262	$554.13	$554.15	$554.10