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 $78.88   9.815%   $86.6221   $86.62   $86.60   $86.60  
  Purchase #2 $208.40   13.348%   $236.2172   $236.22   $236.20   $236.20  
  Purchase #3 $157.28   11.395%   $175.2021   $175.20   $175.20   $175.20  
  Purchase #4 $249.51   6.589%   $265.9502   $265.95   $265.95   $266.00  
  Purchase #5 $23.69   13.657%   $26.9253   $26.93   $26.95   $26.90  
  Purchase #6 $58.48   7.722%   $62.9958   $63.00   $63.00   $63.00  
  Purchase #7 $156.63   4.732%   $164.0417   $164.04   $164.05   $164.00  
  7 purchase totals = $932.87       $1,017.9544   $1,017.96   $1,017.95   $1,017.90