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 $52.52   9.655%   $57.5908   $57.59   $57.60   $57.60  
  Purchase #2 $72.37   9.740%   $79.4188   $79.42   $79.40   $79.40  
  Purchase #3 $175.56   5.349%   $184.9507   $184.95   $184.95   $185.00  
  Purchase #4 $241.77   8.166%   $261.5129   $261.51   $261.50   $261.50  
  Purchase #5 $130.56   12.131%   $146.3982   $146.40   $146.40   $146.40  
  Purchase #6 $146.93   11.222%   $163.4185   $163.42   $163.40   $163.40  
  Purchase #7 $61.27   7.802%   $66.0503   $66.05   $66.05   $66.10  
  7 purchase totals = $880.98       $959.3402   $959.34   $959.30   $959.40