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 $234.69   5.228%   $246.9596   $246.96   $246.95   $247.00  
  Purchase #2 $122.81   11.243%   $136.6175   $136.62   $136.60   $136.60  
  Purchase #3 $52.26   8.674%   $56.793   $56.79   $56.80   $56.80  
  Purchase #4 $228.92   7.111%   $245.1985   $245.20   $245.20   $245.20  
  Purchase #5 $142.72   6.289%   $151.6957   $151.70   $151.70   $151.70  
  Purchase #6 $49.60   12.455%   $55.7777   $55.78   $55.80   $55.80  
  Purchase #7 $51.81   8.378%   $56.1506   $56.15   $56.15   $56.20  
  7 purchase totals = $882.81       $949.1926   $949.20   $949.20   $949.30