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 $59.45   13.370%   $67.3985   $67.40   $67.40   $67.40  
  Purchase #2 $154.72   6.322%   $164.5014   $164.50   $164.50   $164.50  
  Purchase #3 $105.93   5.488%   $111.7434   $111.74   $111.75   $111.70  
  Purchase #4 $24.62   8.604%   $26.7383   $26.74   $26.75   $26.70  
  Purchase #5 $153.71   13.681%   $174.7391   $174.74   $174.75   $174.70  
  Purchase #6 $219.86   11.259%   $244.614   $244.61   $244.60   $244.60  
  Purchase #7 $7.97   12.759%   $8.9869   $8.99   $9.00   $9.00  
  7 purchase totals = $726.26       $798.7216   $798.72   $798.75   $798.60