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 $204.61   5.380%   $215.618   $215.62   $215.60   $215.60  
  Purchase #2 $20.84   13.358%   $23.6238   $23.62   $23.60   $23.60  
  Purchase #3 $122.64   9.551%   $134.3533   $134.35   $134.35   $134.40  
  Purchase #4 $232.72   5.433%   $245.3637   $245.36   $245.35   $245.40  
  Purchase #5 $182.35   10.470%   $201.442   $201.44   $201.45   $201.40  
  Purchase #6 $216.57   8.864%   $235.7668   $235.77   $235.75   $235.80  
  Purchase #7 $187.97   10.806%   $208.282   $208.28   $208.30   $208.30  
  7 purchase totals = $1,167.70       $1,264.4496   $1,264.44   $1,264.40   $1,264.50