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 $114.71   10.217%   $126.4299   $126.43   $126.45   $126.40  
  Purchase #2 $195.58   9.330%   $213.8276   $213.83   $213.85   $213.80  
  Purchase #3 $173.39   3.638%   $179.6979   $179.70   $179.70   $179.70  
  Purchase #4 $60.81   4.455%   $63.5191   $63.52   $63.50   $63.50  
  Purchase #5 $224.28   3.845%   $232.9036   $232.90   $232.90   $232.90  
  Purchase #6 $21.26   9.597%   $23.3003   $23.30   $23.30   $23.30  
  Purchase #7 $41.82   6.151%   $44.3923   $44.39   $44.40   $44.40  
  7 purchase totals = $831.85       $884.0707   $884.07   $884.10   $884.00