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 $90.85   7.476%   $97.6419   $97.64   $97.65   $97.60  
  Purchase #2 $202.89   11.337%   $225.8916   $225.89   $225.90   $225.90  
  Purchase #3 $123.75   8.448%   $134.2044   $134.20   $134.20   $134.20  
  Purchase #4 $71.81   10.391%   $79.2718   $79.27   $79.25   $79.30  
  Purchase #5 $230.63   3.746%   $239.2694   $239.27   $239.25   $239.30  
  Purchase #6 $132.64   10.373%   $146.3987   $146.40   $146.40   $146.40  
  Purchase #7 $69.93   4.766%   $73.2629   $73.26   $73.25   $73.30  
  7 purchase totals = $922.50       $995.9407   $995.93   $995.90   $996.00