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 $59.93   12.328%   $67.3182   $67.32   $67.30   $67.30  
  Purchase #2 $12.27   6.823%   $13.1072   $13.11   $13.10   $13.10  
  Purchase #3 $230.68   7.826%   $248.733   $248.73   $248.75   $248.70  
  Purchase #4 $78.81   7.716%   $84.891   $84.89   $84.90   $84.90  
  Purchase #5 $208.63   4.326%   $217.6553   $217.66   $217.65   $217.70  
  Purchase #6 $26.85   7.560%   $28.8799   $28.88   $28.90   $28.90  
  Purchase #7 $243.69   11.196%   $270.9735   $270.97   $270.95   $271.00  
  7 purchase totals = $860.86       $931.5581   $931.56   $931.55   $931.60