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 $61.87   12.629%   $69.6836   $69.68   $69.70   $69.70  
  Purchase #2 $222.81   12.230%   $250.0597   $250.06   $250.05   $250.10  
  Purchase #3 $10.53   12.605%   $11.8573   $11.86   $11.85   $11.90  
  Purchase #4 $170.34   6.605%   $181.591   $181.59   $181.60   $181.60  
  Purchase #5 $110.44   3.398%   $114.1928   $114.19   $114.20   $114.20  
  Purchase #6 $57.85   6.635%   $61.6883   $61.69   $61.70   $61.70  
  Purchase #7 $152.97   11.227%   $170.1439   $170.14   $170.15   $170.10  
  7 purchase totals = $786.81       $859.2166   $859.21   $859.25   $859.30