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 $65.37   8.183%   $70.7192   $70.72   $70.70   $70.70  
  Purchase #2 $24.87   5.675%   $26.2814   $26.28   $26.30   $26.30  
  Purchase #3 $35.80   3.272%   $36.9714   $36.97   $36.95   $37.00  
  Purchase #4 $23.28   9.655%   $25.5277   $25.53   $25.55   $25.50  
  Purchase #5 $92.76   6.565%   $98.8497   $98.85   $98.85   $98.80  
  Purchase #6 $11.54   3.225%   $11.9122   $11.91   $11.90   $11.90  
  Purchase #7 $5.25   8.413%   $5.6917   $5.69   $5.70   $5.70  
  7 purchase totals = $258.87       $275.9533   $275.95   $275.95   $275.90