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	$164.34	9.528%	$179.9983	$180.00	$180.00	$180.00
Purchase #2	$157.95	13.561%	$179.3696	$179.37	$179.35	$179.40
Purchase #3	$112.82	9.401%	$123.4262	$123.43	$123.45	$123.40
Purchase #4	$24.65	11.559%	$27.4993	$27.50	$27.50	$27.50
Purchase #5	$171.78	6.844%	$183.5366	$183.54	$183.55	$183.50
Purchase #6	$52.85	11.367%	$58.8575	$58.86	$58.85	$58.90
Purchase #7	$229.39	9.807%	$251.8863	$251.89	$251.90	$251.90
7 purchase totals =	$913.78		$1,004.5738	$1,004.59	$1,004.60	$1,004.60