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 $119.86   9.870%   $131.6902   $131.69   $131.70   $131.70  
  Purchase #2 $69.77   7.136%   $74.7488   $74.75   $74.75   $74.70  
  Purchase #3 $102.41   11.556%   $114.2445   $114.24   $114.25   $114.20  
  Purchase #4 $58.82   4.175%   $61.2757   $61.28   $61.30   $61.30  
  Purchase #5 $220.84   6.159%   $234.4415   $234.44   $234.45   $234.40  
  Purchase #6 $217.95   8.806%   $237.1427   $237.14   $237.15   $237.10  
  Purchase #7 $182.74   10.653%   $202.2073   $202.21   $202.20   $202.20  
  7 purchase totals = $972.39       $1,055.7507   $1,055.75   $1,055.80   $1,055.60