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 $56.77   4.186%   $59.1464   $59.15   $59.15   $59.10  
  Purchase #2 $102.84   13.587%   $116.8129   $116.81   $116.80   $116.80  
  Purchase #3 $174.31   5.728%   $184.2945   $184.29   $184.30   $184.30  
  Purchase #4 $200.29   10.249%   $220.8177   $220.82   $220.80   $220.80  
  Purchase #5 $61.56   12.194%   $69.0666   $69.07   $69.05   $69.10  
  Purchase #6 $21.46   11.221%   $23.868   $23.87   $23.85   $23.90  
  Purchase #7 $159.48   12.711%   $179.7515   $179.75   $179.75   $179.80  
  7 purchase totals = $776.71       $853.7576   $853.76   $853.70   $853.80