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 $43.38   5.534%   $45.7806   $45.78   $45.80   $45.80  
  Purchase #2 $133.92   10.276%   $147.6816   $147.68   $147.70   $147.70  
  Purchase #3 $151.70   12.786%   $171.0964   $171.10   $171.10   $171.10  
  Purchase #4 $208.73   6.105%   $221.473   $221.47   $221.45   $221.50  
  Purchase #5 $57.28   9.817%   $62.9032   $62.90   $62.90   $62.90  
  Purchase #6 $78.73   6.770%   $84.06   $84.06   $84.05   $84.10  
  Purchase #7 $216.82   5.349%   $228.4177   $228.42   $228.40   $228.40  
  7 purchase totals = $890.56       $961.4125   $961.41   $961.40   $961.50