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 $215.83   12.554%   $242.9253   $242.93   $242.95   $242.90  
  Purchase #2 $108.26   5.261%   $113.9556   $113.96   $113.95   $114.00  
  Purchase #3 $218.34   6.175%   $231.8225   $231.82   $231.80   $231.80  
  Purchase #4 $49.87   9.291%   $54.5034   $54.50   $54.50   $54.50  
  Purchase #5 $144.86   7.280%   $155.4058   $155.41   $155.40   $155.40  
  Purchase #6 $90.63   13.167%   $102.5633   $102.56   $102.55   $102.60  
  Purchase #7 $115.93   5.367%   $122.152   $122.15   $122.15   $122.20  
  7 purchase totals = $943.72       $1,023.3279   $1,023.33   $1,023.30   $1,023.40