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 $58.63   6.681%   $62.5471   $62.55   $62.55   $62.50  
  Purchase #2 $171.88   5.650%   $181.5912   $181.59   $181.60   $181.60  
  Purchase #3 $210.32   12.338%   $236.2693   $236.27   $236.25   $236.30  
  Purchase #4 $122.51   12.458%   $137.7723   $137.77   $137.75   $137.80  
  Purchase #5 $208.41   13.824%   $237.2206   $237.22   $237.20   $237.20  
  Purchase #6 $182.75   10.127%   $201.2571   $201.26   $201.25   $201.30  
  Purchase #7 $43.91   9.320%   $48.0024   $48.00   $48.00   $48.00  
  7 purchase totals = $998.41       $1,104.6600   $1,104.66   $1,104.60   $1,104.70