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 $24.46   7.153%   $26.2096   $26.21   $26.20   $26.20  
  Purchase #2 $234.83   13.148%   $265.7054   $265.71   $265.70   $265.70  
  Purchase #3 $31.56   12.769%   $35.5899   $35.59   $35.60   $35.60  
  Purchase #4 $204.99   3.221%   $211.5927   $211.59   $211.60   $211.60  
  Purchase #5 $195.84   8.778%   $213.0308   $213.03   $213.05   $213.00  
  Purchase #6 $65.63   6.770%   $70.0732   $70.07   $70.05   $70.10  
  Purchase #7 $179.84   5.859%   $190.3768   $190.38   $190.40   $190.40  
  7 purchase totals = $937.15       $1,012.5784   $1,012.58   $1,012.60   $1,012.60