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 $47.78   10.293%   $52.698   $52.70   $52.70   $52.70  
  Purchase #2 $181.49   12.858%   $204.826   $204.83   $204.85   $204.80  
  Purchase #3 $104.90   7.642%   $112.9165   $112.92   $112.90   $112.90  
  Purchase #4 $159.33   10.444%   $175.9704   $175.97   $175.95   $176.00  
  Purchase #5 $64.44   9.709%   $70.6965   $70.70   $70.70   $70.70  
  Purchase #6 $179.65   4.402%   $187.5582   $187.56   $187.55   $187.60  
  Purchase #7 $99.69   3.194%   $102.8741   $102.87   $102.85   $102.90  
  7 purchase totals = $837.28       $907.5397   $907.55   $907.50   $907.60