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 $48.93   5.531%   $51.6363   $51.64   $51.65   $51.60  
  Purchase #2 $217.60   11.137%   $241.8341   $241.83   $241.85   $241.80  
  Purchase #3 $162.81   10.327%   $179.6234   $179.62   $179.60   $179.60  
  Purchase #4 $71.50   4.851%   $74.9685   $74.97   $74.95   $75.00  
  Purchase #5 $41.73   7.832%   $44.9983   $45.00   $45.00   $45.00  
  Purchase #6 $161.89   13.467%   $183.6917   $183.69   $183.70   $183.70  
  Purchase #7 $162.60   7.451%   $174.7153   $174.72   $174.70   $174.70  
  7 purchase totals = $867.06       $951.4676   $951.47   $951.45   $951.40