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 $43.41   7.296%   $46.5772   $46.58   $46.60   $46.60  
  Purchase #2 $164.63   13.320%   $186.5587   $186.56   $186.55   $186.60  
  Purchase #3 $103.65   9.396%   $113.389   $113.39   $113.40   $113.40  
  Purchase #4 $184.87   12.249%   $207.5147   $207.51   $207.50   $207.50  
  Purchase #5 $155.45   9.607%   $170.3841   $170.38   $170.40   $170.40  
  Purchase #6 $50.58   8.798%   $55.03   $55.03   $55.05   $55.00  
  Purchase #7 $22.85   11.515%   $25.4812   $25.48   $25.50   $25.50  
  7 purchase totals = $725.44       $804.9349   $804.93   $805.00   $805.00