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 $49.72   10.744%   $55.0619   $55.06   $55.05   $55.10  
  Purchase #2 $111.93   13.244%   $126.754   $126.75   $126.75   $126.80  
  Purchase #3 $79.96   7.503%   $85.9594   $85.96   $85.95   $86.00  
  Purchase #4 $11.37   11.552%   $12.6835   $12.68   $12.70   $12.70  
  Purchase #5 $26.63   7.381%   $28.5956   $28.60   $28.60   $28.60  
  Purchase #6 $214.82   10.755%   $237.9239   $237.92   $237.90   $237.90  
  Purchase #7 $101.57   11.353%   $113.1012   $113.10   $113.10   $113.10  
  7 purchase totals = $596.00       $660.0795   $660.07   $660.05   $660.20