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 $86.57   7.531%   $93.0896   $93.09   $93.10   $93.10  
  Purchase #2 $176.26   3.785%   $182.9314   $182.93   $182.95   $182.90  
  Purchase #3 $70.95   13.646%   $80.6318   $80.63   $80.65   $80.60  
  Purchase #4 $218.86   5.524%   $230.9498   $230.95   $230.95   $230.90  
  Purchase #5 $6.54   9.122%   $7.1366   $7.14   $7.15   $7.10  
  Purchase #6 $249.30   11.353%   $277.603   $277.60   $277.60   $277.60  
  Purchase #7 $135.49   4.547%   $141.6507   $141.65   $141.65   $141.70  
  7 purchase totals = $943.97       $1,013.9929   $1,013.99   $1,014.05   $1,013.90