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 $59.77   8.154%   $64.6436   $64.64   $64.65   $64.60  
  Purchase #2 $63.79   10.106%   $70.2366   $70.24   $70.25   $70.20  
  Purchase #3 $196.74   11.647%   $219.6543   $219.65   $219.65   $219.70  
  Purchase #4 $162.78   12.211%   $182.6571   $182.66   $182.65   $182.70  
  Purchase #5 $77.84   7.113%   $83.3768   $83.38   $83.40   $83.40  
  Purchase #6 $246.54   4.797%   $258.3665   $258.37   $258.35   $258.40  
  Purchase #7 $117.36   4.228%   $122.322   $122.32   $122.30   $122.30  
  7 purchase totals = $924.82       $1,001.2569   $1,001.26   $1,001.25   $1,001.30