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 $226.99   5.733%   $240.0033   $240.00   $240.00   $240.00  
  Purchase #2 $156.57   5.164%   $164.6553   $164.66   $164.65   $164.70  
  Purchase #3 $182.57   3.128%   $188.2808   $188.28   $188.30   $188.30  
  Purchase #4 $165.98   5.581%   $175.2433   $175.24   $175.25   $175.20  
  Purchase #5 $231.81   13.521%   $263.153   $263.15   $263.15   $263.20  
  Purchase #6 $165.91   10.640%   $183.5628   $183.56   $183.55   $183.60  
  Purchase #7 $131.60   13.728%   $149.666   $149.67   $149.65   $149.70  
  7 purchase totals = $1,261.43       $1,364.5645   $1,364.56   $1,364.55   $1,364.70