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 $57.61   8.296%   $62.3893   $62.39   $62.40   $62.40  
  Purchase #2 $181.80   11.142%   $202.0562   $202.06   $202.05   $202.10  
  Purchase #3 $249.54   11.484%   $278.1972   $278.20   $278.20   $278.20  
  Purchase #4 $23.87   12.502%   $26.8542   $26.85   $26.85   $26.90  
  Purchase #5 $109.78   12.618%   $123.632   $123.63   $123.65   $123.60  
  Purchase #6 $241.54   8.292%   $261.5685   $261.57   $261.55   $261.60  
  Purchase #7 $134.96   4.847%   $141.5015   $141.50   $141.50   $141.50  
  7 purchase totals = $999.10       $1,096.1989   $1,096.20   $1,096.20   $1,096.30