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 $92.58   6.747%   $98.8264   $98.83   $98.85   $98.80  
  Purchase #2 $239.72   8.330%   $259.6887   $259.69   $259.70   $259.70  
  Purchase #3 $114.69   4.170%   $119.4726   $119.47   $119.45   $119.50  
  Purchase #4 $41.86   3.143%   $43.1757   $43.18   $43.20   $43.20  
  Purchase #5 $118.84   5.360%   $125.2098   $125.21   $125.20   $125.20  
  Purchase #6 $213.44   4.670%   $223.4076   $223.41   $223.40   $223.40  
  Purchase #7 $96.86   9.264%   $105.8331   $105.83   $105.85   $105.80  
  7 purchase totals = $917.99       $975.6139   $975.62   $975.65   $975.60