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 $241.63   6.161%   $256.5168   $256.52   $256.50   $256.50  
  Purchase #2 $230.89   11.699%   $257.9018   $257.90   $257.90   $257.90  
  Purchase #3 $27.69   3.209%   $28.5786   $28.58   $28.60   $28.60  
  Purchase #4 $19.87   5.377%   $20.9384   $20.94   $20.95   $20.90  
  Purchase #5 $116.38   8.347%   $126.0942   $126.09   $126.10   $126.10  
  Purchase #6 $202.76   3.133%   $209.1125   $209.11   $209.10   $209.10  
  Purchase #7 $201.39   12.620%   $226.8054   $226.81   $226.80   $226.80  
  7 purchase totals = $1,040.61       $1,125.9477   $1,125.95   $1,125.95   $1,125.90