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 $23.74   3.546%   $24.5818   $24.58   $24.60   $24.60  
  Purchase #2 $150.43   11.627%   $167.9205   $167.92   $167.90   $167.90  
  Purchase #3 $197.95   11.172%   $220.065   $220.07   $220.05   $220.10  
  Purchase #4 $193.32   4.815%   $202.6284   $202.63   $202.65   $202.60  
  Purchase #5 $127.69   13.666%   $145.1401   $145.14   $145.15   $145.10  
  Purchase #6 $225.69   6.314%   $239.9401   $239.94   $239.95   $239.90  
  Purchase #7 $46.93   3.476%   $48.5613   $48.56   $48.55   $48.60  
  7 purchase totals = $965.75       $1,048.8372   $1,048.84   $1,048.85   $1,048.80