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 $242.86   9.611%   $266.2013   $266.20   $266.20   $266.20  
  Purchase #2 $31.45   4.404%   $32.8351   $32.84   $32.85   $32.80  
  Purchase #3 $196.66   5.441%   $207.3603   $207.36   $207.35   $207.40  
  Purchase #4 $111.80   6.843%   $119.4505   $119.45   $119.45   $119.50  
  Purchase #5 $13.34   6.537%   $14.212   $14.21   $14.20   $14.20  
  Purchase #6 $206.35   13.411%   $234.0236   $234.02   $234.00   $234.00  
  Purchase #7 $72.40   12.143%   $81.1915   $81.19   $81.20   $81.20  
  7 purchase totals = $874.86       $955.2743   $955.27   $955.25   $955.30