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 $36.93   3.597%   $38.2584   $38.26   $38.25   $38.30  
  Purchase #2 $241.95   10.201%   $266.6313   $266.63   $266.65   $266.60  
  Purchase #3 $64.92   8.209%   $70.2493   $70.25   $70.25   $70.20  
  Purchase #4 $126.59   6.602%   $134.9475   $134.95   $134.95   $134.90  
  Purchase #5 $182.71   13.279%   $206.9721   $206.97   $206.95   $207.00  
  Purchase #6 $211.31   10.455%   $233.4025   $233.40   $233.40   $233.40  
  Purchase #7 $176.90   8.850%   $192.5557   $192.56   $192.55   $192.60  
  7 purchase totals = $1,041.31       $1,143.0168   $1,143.02   $1,143.00   $1,143.00