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 $68.81   6.753%   $73.4567   $73.46   $73.45   $73.50  
  Purchase #2 $76.36   7.370%   $81.9877   $81.99   $82.00   $82.00  
  Purchase #3 $15.45   3.862%   $16.0467   $16.05   $16.05   $16.00  
  Purchase #4 $192.93   7.528%   $207.4538   $207.45   $207.45   $207.50  
  Purchase #5 $11.48   5.837%   $12.1501   $12.15   $12.15   $12.20  
  Purchase #6 $243.52   7.532%   $261.8619   $261.86   $261.85   $261.90  
  Purchase #7 $52.63   5.531%   $55.541   $55.54   $55.55   $55.50  
  7 purchase totals = $661.18       $708.4979   $708.50   $708.50   $708.60