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	$140.33	12.516%	$157.8937	$157.89	$157.90	$157.90
Purchase #2	$131.43	6.141%	$139.5011	$139.50	$139.50	$139.50
Purchase #3	$171.47	6.486%	$182.5915	$182.59	$182.60	$182.60
Purchase #4	$124.55	5.712%	$131.6643	$131.66	$131.65	$131.70
Purchase #5	$179.92	7.248%	$192.9606	$192.96	$192.95	$193.00
Purchase #6	$49.94	8.632%	$54.2508	$54.25	$54.25	$54.30
Purchase #7	$90.77	13.201%	$102.7525	$102.75	$102.75	$102.80
7 purchase totals =	$888.41		$961.6145	$961.60	$961.60	$961.80