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 $61.94   5.330%   $65.2414   $65.24   $65.25   $65.20  
  Purchase #2 $61.48   9.305%   $67.2007   $67.20   $67.20   $67.20  
  Purchase #3 $23.95   11.479%   $26.6992   $26.70   $26.70   $26.70  
  Purchase #4 $8.83   10.459%   $9.7535   $9.75   $9.75   $9.80  
  Purchase #5 $224.88   12.555%   $253.1137   $253.11   $253.10   $253.10  
  Purchase #6 $231.78   3.223%   $239.2503   $239.25   $239.25   $239.30  
  Purchase #7 $122.57   3.456%   $126.806   $126.81   $126.80   $126.80  
  7 purchase totals = $735.43       $788.0648   $788.06   $788.05   $788.10