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 $211.92   13.608%   $240.7581   $240.76   $240.75   $240.80  
  Purchase #2 $245.82   10.785%   $272.3317   $272.33   $272.35   $272.30  
  Purchase #3 $136.63   13.270%   $154.7608   $154.76   $154.75   $154.80  
  Purchase #4 $216.39   9.759%   $237.5075   $237.51   $237.50   $237.50  
  Purchase #5 $117.81   5.720%   $124.5487   $124.55   $124.55   $124.50  
  Purchase #6 $61.94   13.451%   $70.2715   $70.27   $70.25   $70.30  
  Purchase #7 $91.44   4.872%   $95.895   $95.90   $95.90   $95.90  
  7 purchase totals = $1,081.95       $1,196.0733   $1,196.08   $1,196.05   $1,196.10