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 $50.90   11.328%   $56.666   $56.67   $56.65   $56.70  
  Purchase #2 $183.26   9.703%   $201.0417   $201.04   $201.05   $201.00  
  Purchase #3 $21.48   11.507%   $23.9517   $23.95   $23.95   $24.00  
  Purchase #4 $197.65   10.655%   $218.7096   $218.71   $218.70   $218.70  
  Purchase #5 $152.73   12.791%   $172.2657   $172.27   $172.25   $172.30  
  Purchase #6 $193.62   9.516%   $212.0449   $212.04   $212.05   $212.00  
  Purchase #7 $75.44   4.755%   $79.0272   $79.03   $79.05   $79.00  
  7 purchase totals = $875.08       $963.7068   $963.71   $963.70   $963.70