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 $213.87   12.673%   $240.9737   $240.97   $240.95   $241.00  
  Purchase #2 $241.84   3.714%   $250.8219   $250.82   $250.80   $250.80  
  Purchase #3 $169.43   7.408%   $181.9814   $181.98   $182.00   $182.00  
  Purchase #4 $248.68   13.644%   $282.6099   $282.61   $282.60   $282.60  
  Purchase #5 $70.47   7.286%   $75.6044   $75.60   $75.60   $75.60  
  Purchase #6 $30.38   10.411%   $33.5429   $33.54   $33.55   $33.50  
  Purchase #7 $230.58   10.587%   $254.9915   $254.99   $255.00   $255.00  
  7 purchase totals = $1,205.25       $1,320.5257   $1,320.51   $1,320.50   $1,320.50