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 $226.69   11.600%   $252.986   $252.99   $253.00   $253.00  
  Purchase #2 $21.67   13.254%   $24.5421   $24.54   $24.55   $24.50  
  Purchase #3 $12.86   13.260%   $14.5652   $14.57   $14.55   $14.60  
  Purchase #4 $202.81   4.841%   $212.628   $212.63   $212.65   $212.60  
  Purchase #5 $127.39   5.221%   $134.041   $134.04   $134.05   $134.00  
  Purchase #6 $105.67   7.244%   $113.3247   $113.32   $113.30   $113.30  
  Purchase #7 $11.69   8.409%   $12.673   $12.67   $12.65   $12.70  
  7 purchase totals = $708.78       $764.7600   $764.76   $764.75   $764.70