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 $56.99   13.340%   $64.5925   $64.59   $64.60   $64.60  
  Purchase #2 $95.49   7.346%   $102.5047   $102.50   $102.50   $102.50  
  Purchase #3 $214.49   4.396%   $223.919   $223.92   $223.90   $223.90  
  Purchase #4 $97.47   11.155%   $108.3428   $108.34   $108.35   $108.30  
  Purchase #5 $156.83   3.267%   $161.9536   $161.95   $161.95   $162.00  
  Purchase #6 $85.90   7.767%   $92.5719   $92.57   $92.55   $92.60  
  Purchase #7 $7.41   8.243%   $8.0208   $8.02   $8.00   $8.00  
  7 purchase totals = $714.58       $761.9053   $761.89   $761.85   $761.90