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 $141.85   6.138%   $150.5568   $150.56   $150.55   $150.60  
  Purchase #2 $75.67   8.286%   $81.94   $81.94   $81.95   $81.90  
  Purchase #3 $112.81   4.190%   $117.5367   $117.54   $117.55   $117.50  
  Purchase #4 $179.38   9.295%   $196.0534   $196.05   $196.05   $196.10  
  Purchase #5 $146.55   10.307%   $161.6549   $161.65   $161.65   $161.70  
  Purchase #6 $155.83   6.499%   $165.9574   $165.96   $165.95   $166.00  
  Purchase #7 $145.99   6.806%   $155.9261   $155.93   $155.95   $155.90  
  7 purchase totals = $958.08       $1,029.6253   $1,029.63   $1,029.65   $1,029.70