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 $227.87   8.577%   $247.4144   $247.41   $247.40   $247.40  
  Purchase #2 $202.57   5.142%   $212.9861   $212.99   $213.00   $213.00  
  Purchase #3 $38.80   13.614%   $44.0822   $44.08   $44.10   $44.10  
  Purchase #4 $125.64   5.269%   $132.26   $132.26   $132.25   $132.30  
  Purchase #5 $134.85   12.177%   $151.2707   $151.27   $151.25   $151.30  
  Purchase #6 $22.45   6.294%   $23.863   $23.86   $23.85   $23.90  
  Purchase #7 $52.56   4.681%   $55.0203   $55.02   $55.00   $55.00  
  7 purchase totals = $804.74       $866.8967   $866.89   $866.85   $867.00