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 $231.79   4.683%   $242.6447   $242.64   $242.65   $242.60  
  Purchase #2 $222.69   4.271%   $232.2011   $232.20   $232.20   $232.20  
  Purchase #3 $157.70   11.543%   $175.9033   $175.90   $175.90   $175.90  
  Purchase #4 $153.55   11.750%   $171.5921   $171.59   $171.60   $171.60  
  Purchase #5 $174.34   8.527%   $189.206   $189.21   $189.20   $189.20  
  Purchase #6 $142.79   5.847%   $151.1389   $151.14   $151.15   $151.10  
  Purchase #7 $9.54   12.432%   $10.726   $10.73   $10.75   $10.70  
  7 purchase totals = $1,092.40       $1,173.4121   $1,173.41   $1,173.45   $1,173.30