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 $67.44   10.280%   $74.3728   $74.37   $74.35   $74.40  
  Purchase #2 $226.89   12.669%   $255.6347   $255.63   $255.65   $255.60  
  Purchase #3 $108.77   5.653%   $114.9188   $114.92   $114.90   $114.90  
  Purchase #4 $80.59   12.869%   $90.9611   $90.96   $90.95   $91.00  
  Purchase #5 $14.69   7.602%   $15.8067   $15.81   $15.80   $15.80  
  Purchase #6 $181.35   10.271%   $199.9765   $199.98   $200.00   $200.00  
  Purchase #7 $228.56   10.706%   $253.0296   $253.03   $253.05   $253.00  
  7 purchase totals = $908.29       $1,004.7002   $1,004.70   $1,004.70   $1,004.70