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 $102.50   11.764%   $114.5581   $114.56   $114.55   $114.60  
  Purchase #2 $236.69   5.761%   $250.3257   $250.33   $250.35   $250.30  
  Purchase #3 $171.38   3.805%   $177.901   $177.90   $177.90   $177.90  
  Purchase #4 $5.87   3.318%   $6.0648   $6.06   $6.05   $6.10  
  Purchase #5 $219.40   4.210%   $228.6367   $228.64   $228.65   $228.60  
  Purchase #6 $29.42   4.185%   $30.6512   $30.65   $30.65   $30.70  
  Purchase #7 $157.36   6.172%   $167.0723   $167.07   $167.05   $167.10  
  7 purchase totals = $922.62       $975.2098   $975.21   $975.20   $975.30