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 $181.61   11.552%   $202.5896   $202.59   $202.60   $202.60  
  Purchase #2 $217.39   8.793%   $236.5051   $236.51   $236.50   $236.50  
  Purchase #3 $63.76   7.190%   $68.3443   $68.34   $68.35   $68.30  
  Purchase #4 $164.33   4.345%   $171.4701   $171.47   $171.45   $171.50  
  Purchase #5 $246.38   6.249%   $261.7763   $261.78   $261.80   $261.80  
  Purchase #6 $167.69   9.821%   $184.1588   $184.16   $184.15   $184.20  
  Purchase #7 $47.46   13.215%   $53.7318   $53.73   $53.75   $53.70  
  7 purchase totals = $1,088.62       $1,178.5760   $1,178.58   $1,178.60   $1,178.60