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 $61.92   7.744%   $66.7151   $66.72   $66.70   $66.70  
  Purchase #2 $246.56   3.208%   $254.4696   $254.47   $254.45   $254.50  
  Purchase #3 $53.36   13.157%   $60.3806   $60.38   $60.40   $60.40  
  Purchase #4 $182.34   10.744%   $201.9306   $201.93   $201.95   $201.90  
  Purchase #5 $247.75   4.641%   $259.2481   $259.25   $259.25   $259.20  
  Purchase #6 $226.92   13.218%   $256.9143   $256.91   $256.90   $256.90  
  Purchase #7 $37.46   10.547%   $41.4109   $41.41   $41.40   $41.40  
  7 purchase totals = $1,056.31       $1,141.0692   $1,141.07   $1,141.05   $1,141.00