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 $50.37   10.249%   $55.5324   $55.53   $55.55   $55.50  
  Purchase #2 $226.85   5.721%   $239.8281   $239.83   $239.85   $239.80  
  Purchase #3 $147.46   6.261%   $156.6925   $156.69   $156.70   $156.70  
  Purchase #4 $190.95   5.382%   $201.2269   $201.23   $201.25   $201.20  
  Purchase #5 $201.39   13.260%   $228.0943   $228.09   $228.10   $228.10  
  Purchase #6 $242.93   3.793%   $252.1443   $252.14   $252.15   $252.10  
  Purchase #7 $72.50   3.448%   $74.9998   $75.00   $75.00   $75.00  
  7 purchase totals = $1,132.45       $1,208.5183   $1,208.51   $1,208.60   $1,208.40