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 $59.39   12.871%   $67.0341   $67.03   $67.05   $67.00  
  Purchase #2 $22.90   3.465%   $23.6935   $23.69   $23.70   $23.70  
  Purchase #3 $198.58   13.597%   $225.5809   $225.58   $225.60   $225.60  
  Purchase #4 $35.88   7.517%   $38.5771   $38.58   $38.60   $38.60  
  Purchase #5 $13.47   5.504%   $14.2114   $14.21   $14.20   $14.20  
  Purchase #6 $130.66   5.539%   $137.8973   $137.90   $137.90   $137.90  
  Purchase #7 $246.99   10.651%   $273.2969   $273.30   $273.30   $273.30  
  7 purchase totals = $707.87       $780.2912   $780.29   $780.35   $780.30