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 $53.70   12.834%   $60.5919   $60.59   $60.60   $60.60  
  Purchase #2 $87.59   6.352%   $93.1537   $93.15   $93.15   $93.20  
  Purchase #3 $31.36   12.874%   $35.3973   $35.40   $35.40   $35.40  
  Purchase #4 $122.65   9.554%   $134.368   $134.37   $134.35   $134.40  
  Purchase #5 $179.70   6.437%   $191.2673   $191.27   $191.25   $191.30  
  Purchase #6 $250.51   8.293%   $271.2848   $271.28   $271.30   $271.30  
  Purchase #7 $166.31   6.350%   $176.8707   $176.87   $176.85   $176.90  
  7 purchase totals = $891.82       $962.9337   $962.93   $962.90   $963.10