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 $119.42   12.432%   $134.2663   $134.27   $134.25   $134.30  
  Purchase #2 $175.82   3.692%   $182.3113   $182.31   $182.30   $182.30  
  Purchase #3 $157.47   11.523%   $175.6153   $175.62   $175.60   $175.60  
  Purchase #4 $44.31   8.781%   $48.2009   $48.20   $48.20   $48.20  
  Purchase #5 $111.61   4.794%   $116.9606   $116.96   $116.95   $117.00  
  Purchase #6 $109.47   12.179%   $122.8024   $122.80   $122.80   $122.80  
  Purchase #7 $128.88   13.372%   $146.1138   $146.11   $146.10   $146.10  
  7 purchase totals = $846.98       $926.2706   $926.27   $926.20   $926.30