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 $118.93   13.133%   $134.5491   $134.55   $134.55   $134.50  
  Purchase #2 $132.71   12.792%   $149.6863   $149.69   $149.70   $149.70  
  Purchase #3 $36.84   7.309%   $39.5326   $39.53   $39.55   $39.50  
  Purchase #4 $184.49   7.619%   $198.5463   $198.55   $198.55   $198.50  
  Purchase #5 $154.67   4.294%   $161.3115   $161.31   $161.30   $161.30  
  Purchase #6 $69.29   9.274%   $75.716   $75.72   $75.70   $75.70  
  Purchase #7 $102.65   3.785%   $106.5353   $106.54   $106.55   $106.50  
  7 purchase totals = $799.58       $865.8771   $865.89   $865.90   $865.70