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 $30.38   10.363%   $33.5283   $33.53   $33.55   $33.50  
  Purchase #2 $233.86   5.454%   $246.6147   $246.61   $246.60   $246.60  
  Purchase #3 $134.49   13.411%   $152.5265   $152.53   $152.55   $152.50  
  Purchase #4 $71.34   13.582%   $81.0294   $81.03   $81.05   $81.00  
  Purchase #5 $246.86   11.723%   $275.7994   $275.80   $275.80   $275.80  
  Purchase #6 $16.50   5.672%   $17.4359   $17.44   $17.45   $17.40  
  Purchase #7 $154.49   6.645%   $164.7559   $164.76   $164.75   $164.80  
  7 purchase totals = $887.92       $971.6901   $971.70   $971.75   $971.60