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 $206.86   13.219%   $234.2048   $234.20   $234.20   $234.20  
  Purchase #2 $242.70   3.849%   $252.0415   $252.04   $252.05   $252.00  
  Purchase #3 $151.48   9.855%   $166.4084   $166.41   $166.40   $166.40  
  Purchase #4 $49.88   13.803%   $56.7649   $56.76   $56.75   $56.80  
  Purchase #5 $116.84   12.178%   $131.0688   $131.07   $131.05   $131.10  
  Purchase #6 $226.33   3.783%   $234.8921   $234.89   $234.90   $234.90  
  Purchase #7 $92.39   12.386%   $103.8334   $103.83   $103.85   $103.80  
  7 purchase totals = $1,086.48       $1,179.2139   $1,179.20   $1,179.20   $1,179.20