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 $58.44   3.802%   $60.6619   $60.66   $60.65   $60.70  
  Purchase #2 $177.45   7.106%   $190.0596   $190.06   $190.05   $190.10  
  Purchase #3 $231.38   12.684%   $260.7282   $260.73   $260.75   $260.70  
  Purchase #4 $65.81   5.496%   $69.4269   $69.43   $69.45   $69.40  
  Purchase #5 $170.85   4.126%   $177.8993   $177.90   $177.90   $177.90  
  Purchase #6 $156.78   8.183%   $169.6093   $169.61   $169.60   $169.60  
  Purchase #7 $77.94   6.119%   $82.7091   $82.71   $82.70   $82.70  
  7 purchase totals = $938.65       $1,011.0943   $1,011.10   $1,011.10   $1,011.10