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 $87.98   12.103%   $98.6282   $98.63   $98.65   $98.60  
  Purchase #2 $166.90   4.696%   $174.7376   $174.74   $174.75   $174.70  
  Purchase #3 $170.38   13.583%   $193.5227   $193.52   $193.50   $193.50  
  Purchase #4 $162.63   8.150%   $175.8843   $175.88   $175.90   $175.90  
  Purchase #5 $83.33   4.769%   $87.304   $87.30   $87.30   $87.30  
  Purchase #6 $15.34   13.695%   $17.4408   $17.44   $17.45   $17.40  
  Purchase #7 $110.70   6.754%   $118.1767   $118.18   $118.20   $118.20  
  7 purchase totals = $797.26       $865.6943   $865.69   $865.75   $865.60