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 $227.41   13.253%   $257.5486   $257.55   $257.55   $257.50  
  Purchase #2 $32.65   8.198%   $35.3266   $35.33   $35.35   $35.30  
  Purchase #3 $96.45   5.462%   $101.7181   $101.72   $101.70   $101.70  
  Purchase #4 $112.85   11.556%   $125.8909   $125.89   $125.90   $125.90  
  Purchase #5 $246.56   5.223%   $259.4378   $259.44   $259.45   $259.40  
  Purchase #6 $7.70   9.622%   $8.4409   $8.44   $8.45   $8.40  
  Purchase #7 $250.67   5.246%   $263.8201   $263.82   $263.80   $263.80  
  7 purchase totals = $974.29       $1,052.1830   $1,052.19   $1,052.20   $1,052.00