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 $188.66   6.124%   $200.2135   $200.21   $200.20   $200.20  
  Purchase #2 $145.93   12.766%   $164.5594   $164.56   $164.55   $164.60  
  Purchase #3 $13.58   8.197%   $14.6932   $14.69   $14.70   $14.70  
  Purchase #4 $50.35   7.752%   $54.2531   $54.25   $54.25   $54.30  
  Purchase #5 $112.85   5.602%   $119.1719   $119.17   $119.15   $119.20  
  Purchase #6 $188.84   4.650%   $197.6211   $197.62   $197.60   $197.60  
  Purchase #7 $240.72   3.109%   $248.204   $248.20   $248.20   $248.20  
  7 purchase totals = $940.93       $998.7162   $998.70   $998.65   $998.80