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 $83.63   13.347%   $94.7921   $94.79   $94.80   $94.80  
  Purchase #2 $15.70   13.128%   $17.7611   $17.76   $17.75   $17.80  
  Purchase #3 $242.73   6.595%   $258.738   $258.74   $258.75   $258.70  
  Purchase #4 $245.99   5.667%   $259.9303   $259.93   $259.95   $259.90  
  Purchase #5 $169.58   13.338%   $192.1986   $192.20   $192.20   $192.20  
  Purchase #6 $199.25   9.307%   $217.7942   $217.79   $217.80   $217.80  
  Purchase #7 $154.57   3.771%   $160.3988   $160.40   $160.40   $160.40  
  7 purchase totals = $1,111.45       $1,201.6131   $1,201.61   $1,201.65   $1,201.60