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 $59.40   3.102%   $61.2426   $61.24   $61.25   $61.20  
  Purchase #2 $194.46   7.127%   $208.3192   $208.32   $208.30   $208.30  
  Purchase #3 $174.42   3.123%   $179.8671   $179.87   $179.85   $179.90  
  Purchase #4 $108.57   8.447%   $117.7409   $117.74   $117.75   $117.70  
  Purchase #5 $112.41   6.775%   $120.0258   $120.03   $120.05   $120.00  
  Purchase #6 $174.80   8.499%   $189.6563   $189.66   $189.65   $189.70  
  Purchase #7 $22.70   7.514%   $24.4057   $24.41   $24.40   $24.40  
  7 purchase totals = $846.76       $901.2576   $901.27   $901.25   $901.20