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 $24.50   7.602%   $26.3625   $26.36   $26.35   $26.40  
  Purchase #2 $118.48   10.323%   $130.7107   $130.71   $130.70   $130.70  
  Purchase #3 $146.84   5.693%   $155.1996   $155.20   $155.20   $155.20  
  Purchase #4 $166.50   11.818%   $186.177   $186.18   $186.20   $186.20  
  Purchase #5 $33.72   7.210%   $36.1512   $36.15   $36.15   $36.20  
  Purchase #6 $186.75   7.746%   $201.2157   $201.22   $201.20   $201.20  
  Purchase #7 $163.92   11.563%   $182.8741   $182.87   $182.85   $182.90  
  7 purchase totals = $840.71       $918.6908   $918.69   $918.65   $918.80