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 $22.44   10.116%   $24.71   $24.71   $24.70   $24.70  
  Purchase #2 $194.50   8.562%   $211.1531   $211.15   $211.15   $211.20  
  Purchase #3 $118.33   11.458%   $131.8883   $131.89   $131.90   $131.90  
  Purchase #4 $165.48   5.822%   $175.1142   $175.11   $175.10   $175.10  
  Purchase #5 $192.47   4.673%   $201.4641   $201.46   $201.45   $201.50  
  Purchase #6 $44.62   4.394%   $46.5806   $46.58   $46.60   $46.60  
  Purchase #7 $159.95   7.465%   $171.8903   $171.89   $171.90   $171.90  
  7 purchase totals = $897.79       $962.8006   $962.79   $962.80   $962.90