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 $228.91   5.694%   $241.9441   $241.94   $241.95   $241.90  
  Purchase #2 $164.48   9.231%   $179.6631   $179.66   $179.65   $179.70  
  Purchase #3 $134.75   8.553%   $146.2752   $146.28   $146.30   $146.30  
  Purchase #4 $33.31   7.707%   $35.8772   $35.88   $35.90   $35.90  
  Purchase #5 $9.84   5.595%   $10.3905   $10.39   $10.40   $10.40  
  Purchase #6 $160.85   9.831%   $176.6632   $176.66   $176.65   $176.70  
  Purchase #7 $68.67   11.237%   $76.3864   $76.39   $76.40   $76.40  
  7 purchase totals = $800.81       $867.1997   $867.20   $867.25   $867.30