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 $85.92   8.448%   $93.1785   $93.18   $93.20   $93.20  
  Purchase #2 $225.38   6.336%   $239.6601   $239.66   $239.65   $239.70  
  Purchase #3 $97.97   7.474%   $105.2923   $105.29   $105.30   $105.30  
  Purchase #4 $161.89   3.405%   $167.4024   $167.40   $167.40   $167.40  
  Purchase #5 $215.62   4.116%   $224.4949   $224.49   $224.50   $224.50  
  Purchase #6 $162.63   6.524%   $173.24   $173.24   $173.25   $173.20  
  Purchase #7 $156.52   7.263%   $167.888   $167.89   $167.90   $167.90  
  7 purchase totals = $1,105.93       $1,171.1562   $1,171.15   $1,171.20   $1,171.20