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 $56.58   11.545%   $63.1122   $63.11   $63.10   $63.10  
  Purchase #2 $98.89   6.321%   $105.1408   $105.14   $105.15   $105.10  
  Purchase #3 $23.67   13.273%   $26.8117   $26.81   $26.80   $26.80  
  Purchase #4 $25.27   13.403%   $28.6569   $28.66   $28.65   $28.70  
  Purchase #5 $238.73   8.687%   $259.4685   $259.47   $259.45   $259.50  
  Purchase #6 $32.72   10.176%   $36.0496   $36.05   $36.05   $36.00  
  Purchase #7 $219.80   7.403%   $236.0718   $236.07   $236.05   $236.10  
  7 purchase totals = $695.66       $755.3115   $755.31   $755.25   $755.30