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 $8.61   11.725%   $9.6195   $9.62   $9.60   $9.60  
  Purchase #2 $237.39   12.157%   $266.2495   $266.25   $266.25   $266.20  
  Purchase #3 $131.60   12.614%   $148.2   $148.20   $148.20   $148.20  
  Purchase #4 $10.91   3.396%   $11.2805   $11.28   $11.30   $11.30  
  Purchase #5 $211.41   11.163%   $235.0097   $235.01   $235.00   $235.00  
  Purchase #6 $25.69   3.488%   $26.5861   $26.59   $26.60   $26.60  
  Purchase #7 $75.46   7.782%   $81.3323   $81.33   $81.35   $81.30  
  7 purchase totals = $701.07       $778.2776   $778.28   $778.30   $778.20