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 $116.63   8.426%   $126.4572   $126.46   $126.45   $126.50  
  Purchase #2 $184.72   5.156%   $194.2442   $194.24   $194.25   $194.20  
  Purchase #3 $151.95   4.350%   $158.5598   $158.56   $158.55   $158.60  
  Purchase #4 $175.50   11.490%   $195.665   $195.67   $195.65   $195.70  
  Purchase #5 $179.84   7.551%   $193.4197   $193.42   $193.40   $193.40  
  Purchase #6 $70.99   9.849%   $77.9818   $77.98   $78.00   $78.00  
  Purchase #7 $56.34   4.428%   $58.8347   $58.83   $58.85   $58.80  
  7 purchase totals = $935.97       $1,005.1624   $1,005.16   $1,005.15   $1,005.20