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 $242.80   6.772%   $259.2424   $259.24   $259.25   $259.20  
  Purchase #2 $132.53   7.621%   $142.6301   $142.63   $142.65   $142.60  
  Purchase #3 $126.77   8.459%   $137.4935   $137.49   $137.50   $137.50  
  Purchase #4 $189.86   4.808%   $198.9885   $198.99   $199.00   $199.00  
  Purchase #5 $233.72   7.791%   $251.9291   $251.93   $251.95   $251.90  
  Purchase #6 $201.51   6.414%   $214.4349   $214.43   $214.45   $214.40  
  Purchase #7 $52.68   11.715%   $58.8515   $58.85   $58.85   $58.90  
  7 purchase totals = $1,179.87       $1,263.5700   $1,263.56   $1,263.65   $1,263.50