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 $206.29   11.282%   $229.5636   $229.56   $229.55   $229.60  
  Purchase #2 $216.25   6.192%   $229.6402   $229.64   $229.65   $229.60  
  Purchase #3 $65.42   6.630%   $69.7573   $69.76   $69.75   $69.80  
  Purchase #4 $177.26   5.306%   $186.6654   $186.67   $186.65   $186.70  
  Purchase #5 $234.88   4.554%   $245.5764   $245.58   $245.60   $245.60  
  Purchase #6 $95.93   5.136%   $100.857   $100.86   $100.85   $100.90  
  Purchase #7 $250.65   8.844%   $272.8175   $272.82   $272.80   $272.80  
  7 purchase totals = $1,246.68       $1,334.8774   $1,334.89   $1,334.85   $1,335.00