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 $88.34   8.194%   $95.5786   $95.58   $95.60   $95.60  
  Purchase #2 $197.64   11.122%   $219.6215   $219.62   $219.60   $219.60  
  Purchase #3 $114.87   7.163%   $123.0981   $123.10   $123.10   $123.10  
  Purchase #4 $93.28   11.129%   $103.6611   $103.66   $103.65   $103.70  
  Purchase #5 $136.92   4.842%   $143.5497   $143.55   $143.55   $143.50  
  Purchase #6 $56.74   8.279%   $61.4375   $61.44   $61.45   $61.40  
  Purchase #7 $238.84   5.610%   $252.2389   $252.24   $252.25   $252.20  
  7 purchase totals = $926.63       $999.1854   $999.19   $999.20   $999.10