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 $76.62   10.815%   $84.9065   $84.91   $84.90   $84.90  
  Purchase #2 $34.43   9.298%   $37.6313   $37.63   $37.65   $37.60  
  Purchase #3 $72.60   12.759%   $81.863   $81.86   $81.85   $81.90  
  Purchase #4 $212.91   3.581%   $220.5343   $220.53   $220.55   $220.50  
  Purchase #5 $122.72   8.235%   $132.826   $132.83   $132.85   $132.80  
  Purchase #6 $160.26   10.853%   $177.653   $177.65   $177.65   $177.70  
  Purchase #7 $19.32   13.477%   $21.9238   $21.92   $21.90   $21.90  
  7 purchase totals = $698.86       $757.3379   $757.33   $757.35   $757.30