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 $32.87   9.298%   $35.9263   $35.93   $35.95   $35.90  
  Purchase #2 $16.93   8.441%   $18.3591   $18.36   $18.35   $18.40  
  Purchase #3 $104.53   8.723%   $113.6482   $113.65   $113.65   $113.60  
  Purchase #4 $120.31   12.115%   $134.8856   $134.89   $134.90   $134.90  
  Purchase #5 $191.99   10.550%   $212.2449   $212.24   $212.25   $212.20  
  Purchase #6 $34.45   3.582%   $35.684   $35.68   $35.70   $35.70  
  Purchase #7 $154.40   12.412%   $173.5641   $173.56   $173.55   $173.60  
  7 purchase totals = $655.48       $724.3122   $724.31   $724.35   $724.30