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 $209.49   3.136%   $216.0596   $216.06   $216.05   $216.10  
  Purchase #2 $91.73   4.276%   $95.6524   $95.65   $95.65   $95.70  
  Purchase #3 $105.54   10.203%   $116.3082   $116.31   $116.30   $116.30  
  Purchase #4 $78.38   10.874%   $86.903   $86.90   $86.90   $86.90  
  Purchase #5 $31.56   12.411%   $35.4769   $35.48   $35.50   $35.50  
  Purchase #6 $56.36   9.429%   $61.6742   $61.67   $61.65   $61.70  
  Purchase #7 $192.93   11.646%   $215.3986   $215.40   $215.40   $215.40  
  7 purchase totals = $765.99       $827.4729   $827.47   $827.45   $827.60