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	$26.76	6.439%	$28.4831	$28.48	$28.50	$28.50
Purchase #2	$70.79	11.115%	$78.6583	$78.66	$78.65	$78.70
Purchase #3	$87.99	5.605%	$92.9218	$92.92	$92.90	$92.90
Purchase #4	$29.34	5.474%	$30.9461	$30.95	$30.95	$30.90
Purchase #5	$156.59	9.490%	$171.4504	$171.45	$171.45	$171.50
Purchase #6	$73.81	9.672%	$80.9489	$80.95	$80.95	$80.90
Purchase #7	$172.78	5.557%	$182.3814	$182.38	$182.40	$182.40
7 purchase totals =	$618.06		$665.7900	$665.79	$665.80	$665.80