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 $56.34   8.756%   $61.2731   $61.27   $61.25   $61.30  
  Purchase #2 $221.43   3.498%   $229.1756   $229.18   $229.20   $229.20  
  Purchase #3 $46.72   10.715%   $51.726   $51.73   $51.75   $51.70  
  Purchase #4 $23.73   4.637%   $24.8304   $24.83   $24.85   $24.80  
  Purchase #5 $108.96   12.622%   $122.7129   $122.71   $122.70   $122.70  
  Purchase #6 $47.33   4.831%   $49.6165   $49.62   $49.60   $49.60  
  Purchase #7 $67.48   6.592%   $71.9283   $71.93   $71.95   $71.90  
  7 purchase totals = $571.99       $611.2628   $611.27   $611.30   $611.20