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 $56.50   12.618%   $63.6292   $63.63   $63.65   $63.60  
  Purchase #2 $157.48   12.434%   $177.0611   $177.06   $177.05   $177.10  
  Purchase #3 $178.67   13.455%   $202.71   $202.71   $202.70   $202.70  
  Purchase #4 $210.92   9.802%   $231.5944   $231.59   $231.60   $231.60  
  Purchase #5 $35.60   10.311%   $39.2707   $39.27   $39.25   $39.30  
  Purchase #6 $91.77   3.534%   $95.0132   $95.01   $95.00   $95.00  
  Purchase #7 $11.93   11.324%   $13.281   $13.28   $13.30   $13.30  
  7 purchase totals = $742.87       $822.5596   $822.55   $822.55   $822.60