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 $24.90   6.455%   $26.5073   $26.51   $26.50   $26.50  
  Purchase #2 $199.51   9.380%   $218.224   $218.22   $218.20   $218.20  
  Purchase #3 $244.66   10.713%   $270.8704   $270.87   $270.85   $270.90  
  Purchase #4 $219.65   11.668%   $245.2788   $245.28   $245.30   $245.30  
  Purchase #5 $23.62   5.769%   $24.9826   $24.98   $25.00   $25.00  
  Purchase #6 $15.73   13.699%   $17.8849   $17.88   $17.90   $17.90  
  Purchase #7 $219.47   9.205%   $239.6722   $239.67   $239.65   $239.70  
  7 purchase totals = $947.54       $1,043.4202   $1,043.41   $1,043.40   $1,043.50