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 $245.98   6.466%   $261.8851   $261.89   $261.90   $261.90  
  Purchase #2 $14.94   9.445%   $16.3511   $16.35   $16.35   $16.40  
  Purchase #3 $71.57   6.282%   $76.066   $76.07   $76.05   $76.10  
  Purchase #4 $51.38   4.453%   $53.668   $53.67   $53.65   $53.70  
  Purchase #5 $15.73   8.836%   $17.1199   $17.12   $17.10   $17.10  
  Purchase #6 $199.61   6.633%   $212.8501   $212.85   $212.85   $212.90  
  Purchase #7 $155.67   10.773%   $172.4403   $172.44   $172.45   $172.40  
  7 purchase totals = $754.88       $810.3805   $810.39   $810.35   $810.50