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 $225.25   3.273%   $232.6224   $232.62   $232.60   $232.60  
  Purchase #2 $191.87   8.681%   $208.5262   $208.53   $208.55   $208.50  
  Purchase #3 $67.61   13.766%   $76.9172   $76.92   $76.90   $76.90  
  Purchase #4 $105.39   4.118%   $109.73   $109.73   $109.75   $109.70  
  Purchase #5 $167.87   3.653%   $174.0023   $174.00   $174.00   $174.00  
  Purchase #6 $99.40   10.504%   $109.841   $109.84   $109.85   $109.80  
  Purchase #7 $36.70   4.211%   $38.2454   $38.25   $38.25   $38.20  
  7 purchase totals = $894.09       $949.8845   $949.89   $949.90   $949.70