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 $179.46   12.515%   $201.9194   $201.92   $201.90   $201.90  
  Purchase #2 $148.42   12.624%   $167.1565   $167.16   $167.15   $167.20  
  Purchase #3 $21.90   9.617%   $24.0061   $24.01   $24.00   $24.00  
  Purchase #4 $235.63   12.756%   $265.687   $265.69   $265.70   $265.70  
  Purchase #5 $229.92   4.355%   $239.933   $239.93   $239.95   $239.90  
  Purchase #6 $200.49   11.500%   $223.5464   $223.55   $223.55   $223.50  
  Purchase #7 $94.95   6.583%   $101.2006   $101.20   $101.20   $101.20  
  7 purchase totals = $1,110.77       $1,223.4490   $1,223.46   $1,223.45   $1,223.40