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 $211.27   10.632%   $233.7322   $233.73   $233.75   $233.70  
  Purchase #2 $14.59   8.723%   $15.8627   $15.86   $15.85   $15.90  
  Purchase #3 $62.78   12.724%   $70.7681   $70.77   $70.75   $70.80  
  Purchase #4 $218.84   3.732%   $227.0071   $227.01   $227.00   $227.00  
  Purchase #5 $69.44   10.203%   $76.525   $76.53   $76.55   $76.50  
  Purchase #6 $147.44   4.551%   $154.15   $154.15   $154.15   $154.20  
  Purchase #7 $51.67   6.681%   $55.1221   $55.12   $55.10   $55.10  
  7 purchase totals = $776.03       $833.1672   $833.17   $833.15   $833.20