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 $192.72   6.422%   $205.0965   $205.10   $205.10   $205.10  
  Purchase #2 $242.27   10.587%   $267.9191   $267.92   $267.90   $267.90  
  Purchase #3 $187.83   5.228%   $197.6498   $197.65   $197.65   $197.60  
  Purchase #4 $73.54   6.848%   $78.576   $78.58   $78.60   $78.60  
  Purchase #5 $115.31   12.273%   $129.462   $129.46   $129.45   $129.50  
  Purchase #6 $48.40   8.587%   $52.5561   $52.56   $52.55   $52.60  
  Purchase #7 $85.80   7.289%   $92.054   $92.05   $92.05   $92.10  
  7 purchase totals = $945.87       $1,023.3135   $1,023.32   $1,023.30   $1,023.40