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 $55.81   6.119%   $59.225   $59.23   $59.25   $59.20  
  Purchase #2 $83.61   9.516%   $91.5663   $91.57   $91.55   $91.60  
  Purchase #3 $64.26   9.379%   $70.2869   $70.29   $70.30   $70.30  
  Purchase #4 $144.29   8.731%   $156.888   $156.89   $156.90   $156.90  
  Purchase #5 $153.40   9.407%   $167.8303   $167.83   $167.85   $167.80  
  Purchase #6 $186.42   11.558%   $207.9664   $207.97   $207.95   $208.00  
  Purchase #7 $179.30   12.350%   $201.4436   $201.44   $201.45   $201.40  
  7 purchase totals = $867.09       $955.2065   $955.22   $955.25   $955.20