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 $236.38   5.179%   $248.6221   $248.62   $248.60   $248.60  
  Purchase #2 $240.69   11.157%   $267.5438   $267.54   $267.55   $267.50  
  Purchase #3 $21.40   11.394%   $23.8383   $23.84   $23.85   $23.80  
  Purchase #4 $246.62   10.213%   $271.8073   $271.81   $271.80   $271.80  
  Purchase #5 $153.69   5.281%   $161.8064   $161.81   $161.80   $161.80  
  Purchase #6 $13.57   12.109%   $15.2132   $15.21   $15.20   $15.20  
  Purchase #7 $33.32   10.528%   $36.8279   $36.83   $36.85   $36.80  
  7 purchase totals = $945.67       $1,025.6590   $1,025.66   $1,025.65   $1,025.50