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 $55.85   10.160%   $61.5244   $61.52   $61.50   $61.50  
  Purchase #2 $46.32   6.151%   $49.1691   $49.17   $49.15   $49.20  
  Purchase #3 $236.81   10.398%   $261.4335   $261.43   $261.45   $261.40  
  Purchase #4 $248.95   4.692%   $260.6307   $260.63   $260.65   $260.60  
  Purchase #5 $49.73   11.113%   $55.2565   $55.26   $55.25   $55.30  
  Purchase #6 $188.50   13.258%   $213.4913   $213.49   $213.50   $213.50  
  Purchase #7 $178.91   13.708%   $203.435   $203.44   $203.45   $203.40  
  7 purchase totals = $1,005.07       $1,104.9405   $1,104.94   $1,104.95   $1,104.90