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 $246.26   8.652%   $267.5664   $267.57   $267.55   $267.60  
  Purchase #2 $125.53   11.183%   $139.568   $139.57   $139.55   $139.60  
  Purchase #3 $8.54   4.563%   $8.9297   $8.93   $8.95   $8.90  
  Purchase #4 $206.39   3.418%   $213.4444   $213.44   $213.45   $213.40  
  Purchase #5 $61.84   3.272%   $63.8634   $63.86   $63.85   $63.90  
  Purchase #6 $31.75   5.851%   $33.6077   $33.61   $33.60   $33.60  
  Purchase #7 $190.82   4.409%   $199.2333   $199.23   $199.25   $199.20  
  7 purchase totals = $871.13       $926.2129   $926.21   $926.20   $926.20