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 $21.93   7.614%   $23.5998   $23.60   $23.60   $23.60  
  Purchase #2 $223.65   11.856%   $250.1659   $250.17   $250.15   $250.20  
  Purchase #3 $72.77   3.809%   $75.5418   $75.54   $75.55   $75.50  
  Purchase #4 $141.47   10.542%   $156.3838   $156.38   $156.40   $156.40  
  Purchase #5 $233.45   7.387%   $250.695   $250.70   $250.70   $250.70  
  Purchase #6 $137.85   3.683%   $142.927   $142.93   $142.95   $142.90  
  Purchase #7 $61.42   11.846%   $68.6958   $68.70   $68.70   $68.70  
  7 purchase totals = $892.54       $968.0091   $968.02   $968.05   $968.00