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 $57.34   13.300%   $64.9662   $64.97   $64.95   $65.00  
  Purchase #2 $25.69   4.399%   $26.8201   $26.82   $26.80   $26.80  
  Purchase #3 $60.65   11.334%   $67.5241   $67.52   $67.50   $67.50  
  Purchase #4 $206.51   9.457%   $226.0397   $226.04   $226.05   $226.00  
  Purchase #5 $126.61   8.652%   $137.5643   $137.56   $137.55   $137.60  
  Purchase #6 $190.44   13.782%   $216.6864   $216.69   $216.70   $216.70  
  Purchase #7 $27.88   3.271%   $28.792   $28.79   $28.80   $28.80  
  7 purchase totals = $695.12       $768.3928   $768.39   $768.35   $768.40