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 $91.73   4.312%   $95.6854   $95.69   $95.70   $95.70  
  Purchase #2 $222.40   5.503%   $234.6387   $234.64   $234.65   $234.60  
  Purchase #3 $64.49   4.600%   $67.4565   $67.46   $67.45   $67.50  
  Purchase #4 $111.68   5.597%   $117.9307   $117.93   $117.95   $117.90  
  Purchase #5 $60.91   5.696%   $64.3794   $64.38   $64.40   $64.40  
  Purchase #6 $14.88   6.414%   $15.8344   $15.83   $15.85   $15.80  
  Purchase #7 $141.92   3.447%   $146.812   $146.81   $146.80   $146.80  
  7 purchase totals = $708.01       $742.7371   $742.74   $742.80   $742.70