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 $84.71   10.266%   $93.4063   $93.41   $93.40   $93.40  
  Purchase #2 $168.76   5.436%   $177.9338   $177.93   $177.95   $177.90  
  Purchase #3 $108.72   7.247%   $116.5989   $116.60   $116.60   $116.60  
  Purchase #4 $231.25   13.782%   $263.1209   $263.12   $263.10   $263.10  
  Purchase #5 $203.45   5.672%   $214.9897   $214.99   $215.00   $215.00  
  Purchase #6 $24.40   9.373%   $26.687   $26.69   $26.70   $26.70  
  Purchase #7 $127.94   4.557%   $133.7702   $133.77   $133.75   $133.80  
  7 purchase totals = $949.23       $1,026.5068   $1,026.51   $1,026.50   $1,026.50