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 $20.48   10.750%   $22.6816   $22.68   $22.70   $22.70  
  Purchase #2 $178.81   12.411%   $201.0021   $201.00   $201.00   $201.00  
  Purchase #3 $21.90   13.108%   $24.7707   $24.77   $24.75   $24.80  
  Purchase #4 $245.51   9.741%   $269.4251   $269.43   $269.45   $269.40  
  Purchase #5 $23.75   4.656%   $24.8558   $24.86   $24.85   $24.90  
  Purchase #6 $154.57   5.697%   $163.3759   $163.38   $163.40   $163.40  
  Purchase #7 $237.25   8.238%   $256.7947   $256.79   $256.80   $256.80  
  7 purchase totals = $882.27       $962.9059   $962.91   $962.95   $963.00