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 $60.66   9.108%   $66.1849   $66.18   $66.20   $66.20  
  Purchase #2 $228.41   12.832%   $257.7196   $257.72   $257.70   $257.70  
  Purchase #3 $173.90   12.403%   $195.4688   $195.47   $195.45   $195.50  
  Purchase #4 $50.86   3.867%   $52.8268   $52.83   $52.85   $52.80  
  Purchase #5 $122.61   13.459%   $139.1121   $139.11   $139.10   $139.10  
  Purchase #6 $109.85   12.135%   $123.1803   $123.18   $123.20   $123.20  
  Purchase #7 $214.71   8.714%   $233.4198   $233.42   $233.40   $233.40  
  7 purchase totals = $961.00       $1,067.9123   $1,067.91   $1,067.90   $1,067.90