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 $56.31   8.799%   $61.2647   $61.26   $61.25   $61.30  
  Purchase #2 $51.44   7.789%   $55.4467   $55.45   $55.45   $55.40  
  Purchase #3 $18.46   4.608%   $19.3106   $19.31   $19.30   $19.30  
  Purchase #4 $15.29   13.328%   $17.3279   $17.33   $17.35   $17.30  
  Purchase #5 $197.72   5.183%   $207.9678   $207.97   $207.95   $208.00  
  Purchase #6 $68.49   12.783%   $77.2451   $77.25   $77.25   $77.20  
  Purchase #7 $150.59   5.581%   $158.9944   $158.99   $159.00   $159.00  
  7 purchase totals = $558.30       $597.5572   $597.56   $597.55   $597.50