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 $237.94   11.851%   $266.1383   $266.14   $266.15   $266.10  
  Purchase #2 $191.56   5.405%   $201.9138   $201.91   $201.90   $201.90  
  Purchase #3 $24.94   6.657%   $26.6003   $26.60   $26.60   $26.60  
  Purchase #4 $162.51   8.437%   $176.221   $176.22   $176.20   $176.20  
  Purchase #5 $57.93   9.436%   $63.3963   $63.40   $63.40   $63.40  
  Purchase #6 $59.51   10.795%   $65.9341   $65.93   $65.95   $65.90  
  Purchase #7 $96.50   7.268%   $103.5136   $103.51   $103.50   $103.50  
  7 purchase totals = $830.89       $903.7174   $903.71   $903.70   $903.60