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	$162.73	10.303%	$179.4961	$179.50	$179.50	$179.50
Purchase #2	$59.33	7.628%	$63.8557	$63.86	$63.85	$63.90
Purchase #3	$199.78	6.814%	$213.393	$213.39	$213.40	$213.40
Purchase #4	$168.26	13.226%	$190.5141	$190.51	$190.50	$190.50
Purchase #5	$26.40	4.713%	$27.6442	$27.64	$27.65	$27.60
Purchase #6	$57.66	9.402%	$63.0812	$63.08	$63.10	$63.10
Purchase #7	$107.34	4.818%	$112.5116	$112.51	$112.50	$112.50
7 purchase totals =	$781.50		$850.4959	$850.49	$850.50	$850.50