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 $248.87   13.618%   $282.7611   $282.76   $282.75   $282.80  
  Purchase #2 $237.25   11.867%   $265.4045   $265.40   $265.40   $265.40  
  Purchase #3 $82.39   5.159%   $86.6405   $86.64   $86.65   $86.60  
  Purchase #4 $91.88   5.842%   $97.2476   $97.25   $97.25   $97.20  
  Purchase #5 $234.43   3.539%   $242.7265   $242.73   $242.75   $242.70  
  Purchase #6 $157.73   5.673%   $166.678   $166.68   $166.70   $166.70  
  Purchase #7 $25.75   11.868%   $28.806   $28.81   $28.80   $28.80  
  7 purchase totals = $1,078.30       $1,170.2642   $1,170.27   $1,170.30   $1,170.20