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 $89.42   4.790%   $93.7032   $93.70   $93.70   $93.70  
  Purchase #2 $170.49   13.411%   $193.3544   $193.35   $193.35   $193.40  
  Purchase #3 $66.69   7.569%   $71.7378   $71.74   $71.75   $71.70  
  Purchase #4 $183.91   10.568%   $203.3456   $203.35   $203.35   $203.30  
  Purchase #5 $43.30   8.631%   $47.0372   $47.04   $47.05   $47.00  
  Purchase #6 $163.30   6.787%   $174.3832   $174.38   $174.40   $174.40  
  Purchase #7 $76.86   3.514%   $79.5609   $79.56   $79.55   $79.60  
  7 purchase totals = $793.97       $863.1223   $863.12   $863.15   $863.10