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 $231.35   4.269%   $241.2263   $241.23   $241.25   $241.20  
  Purchase #2 $61.52   10.114%   $67.7421   $67.74   $67.75   $67.70  
  Purchase #3 $196.47   6.657%   $209.549   $209.55   $209.55   $209.50  
  Purchase #4 $132.52   7.767%   $142.8128   $142.81   $142.80   $142.80  
  Purchase #5 $161.97   4.789%   $169.7267   $169.73   $169.75   $169.70  
  Purchase #6 $23.66   10.681%   $26.1871   $26.19   $26.20   $26.20  
  Purchase #7 $93.58   5.525%   $98.7503   $98.75   $98.75   $98.80  
  7 purchase totals = $901.07       $955.9943   $956.00   $956.05   $955.90