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 $65.44   5.208%   $68.8481   $68.85   $68.85   $68.80  
  Purchase #2 $220.43   4.282%   $229.8688   $229.87   $229.85   $229.90  
  Purchase #3 $216.49   13.395%   $245.4888   $245.49   $245.50   $245.50  
  Purchase #4 $245.42   5.770%   $259.5807   $259.58   $259.60   $259.60  
  Purchase #5 $217.47   3.671%   $225.4533   $225.45   $225.45   $225.50  
  Purchase #6 $47.81   12.775%   $53.9177   $53.92   $53.90   $53.90  
  Purchase #7 $179.47   4.815%   $188.1115   $188.11   $188.10   $188.10  
  7 purchase totals = $1,192.53       $1,271.2689   $1,271.27   $1,271.25   $1,271.30