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 $208.38   11.716%   $232.7938   $232.79   $232.80   $232.80  
  Purchase #2 $80.62   3.874%   $83.7432   $83.74   $83.75   $83.70  
  Purchase #3 $28.30   12.802%   $31.923   $31.92   $31.90   $31.90  
  Purchase #4 $48.76   3.737%   $50.5822   $50.58   $50.60   $50.60  
  Purchase #5 $219.33   8.374%   $237.6967   $237.70   $237.70   $237.70  
  Purchase #6 $92.70   12.435%   $104.2272   $104.23   $104.25   $104.20  
  Purchase #7 $152.25   7.751%   $164.0509   $164.05   $164.05   $164.10  
  7 purchase totals = $830.34       $905.0170   $905.01   $905.05   $905.00