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 $14.32   12.135%   $16.0577   $16.06   $16.05   $16.10  
  Purchase #2 $201.94   3.187%   $208.3758   $208.38   $208.40   $208.40  
  Purchase #3 $71.81   13.733%   $81.6717   $81.67   $81.65   $81.70  
  Purchase #4 $210.93   4.244%   $219.8819   $219.88   $219.90   $219.90  
  Purchase #5 $247.65   11.159%   $275.2853   $275.29   $275.30   $275.30  
  Purchase #6 $142.64   12.184%   $160.0193   $160.02   $160.00   $160.00  
  Purchase #7 $76.76   11.352%   $85.4738   $85.47   $85.45   $85.50  
  7 purchase totals = $966.05       $1,046.7655   $1,046.77   $1,046.75   $1,046.90