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 $60.83   12.629%   $68.5122   $68.51   $68.50   $68.50  
  Purchase #2 $236.65   7.213%   $253.7196   $253.72   $253.70   $253.70  
  Purchase #3 $224.48   4.680%   $234.9857   $234.99   $235.00   $235.00  
  Purchase #4 $236.41   13.445%   $268.1953   $268.20   $268.20   $268.20  
  Purchase #5 $184.67   12.105%   $207.0243   $207.02   $207.00   $207.00  
  Purchase #6 $80.85   6.380%   $86.0082   $86.01   $86.00   $86.00  
  Purchase #7 $72.87   7.110%   $78.0511   $78.05   $78.05   $78.10  
  7 purchase totals = $1,096.76       $1,196.4964   $1,196.50   $1,196.45   $1,196.50