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 $176.90   13.151%   $200.1641   $200.16   $200.15   $200.20  
  Purchase #2 $138.57   11.446%   $154.4307   $154.43   $154.45   $154.40  
  Purchase #3 $39.38   12.226%   $44.1946   $44.19   $44.20   $44.20  
  Purchase #4 $136.33   11.272%   $151.6971   $151.70   $151.70   $151.70  
  Purchase #5 $84.40   4.645%   $88.3204   $88.32   $88.30   $88.30  
  Purchase #6 $183.36   8.500%   $198.9456   $198.95   $198.95   $198.90  
  Purchase #7 $164.59   12.706%   $185.5028   $185.50   $185.50   $185.50  
  7 purchase totals = $923.53       $1,023.2553   $1,023.25   $1,023.25   $1,023.20