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	$132.25	9.261%	$144.4977	$144.50	$144.50	$144.50
Purchase #2	$19.99	6.732%	$21.3357	$21.34	$21.35	$21.30
Purchase #3	$58.47	12.672%	$65.8793	$65.88	$65.90	$65.90
Purchase #4	$83.81	6.461%	$89.225	$89.23	$89.25	$89.20
Purchase #5	$116.37	7.323%	$124.8918	$124.89	$124.90	$124.90
Purchase #6	$227.83	13.206%	$257.9172	$257.92	$257.90	$257.90
Purchase #7	$244.80	11.760%	$273.5885	$273.59	$273.60	$273.60
7 purchase totals =	$883.52		$977.3352	$977.35	$977.40	$977.30