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 $222.80   13.399%   $252.653   $252.65   $252.65   $252.70  
  Purchase #2 $7.83   7.226%   $8.3958   $8.40   $8.40   $8.40  
  Purchase #3 $201.56   8.419%   $218.5293   $218.53   $218.55   $218.50  
  Purchase #4 $60.75   11.549%   $67.766   $67.77   $67.75   $67.80  
  Purchase #5 $193.83   9.709%   $212.649   $212.65   $212.65   $212.60  
  Purchase #6 $147.73   7.542%   $158.8718   $158.87   $158.85   $158.90  
  Purchase #7 $43.97   7.524%   $47.2783   $47.28   $47.30   $47.30  
  7 purchase totals = $878.47       $966.1432   $966.15   $966.15   $966.20