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 $57.60   10.233%   $63.4942   $63.49   $63.50   $63.50  
  Purchase #2 $224.51   4.120%   $233.7598   $233.76   $233.75   $233.80  
  Purchase #3 $116.93   12.617%   $131.6831   $131.68   $131.70   $131.70  
  Purchase #4 $59.26   11.759%   $66.2284   $66.23   $66.25   $66.20  
  Purchase #5 $208.91   13.412%   $236.929   $236.93   $236.95   $236.90  
  Purchase #6 $113.57   11.804%   $126.9758   $126.98   $127.00   $127.00  
  Purchase #7 $166.84   13.718%   $189.7271   $189.73   $189.75   $189.70  
  7 purchase totals = $947.62       $1,048.7974   $1,048.80   $1,048.90   $1,048.80