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 $55.92   12.397%   $62.8524   $62.85   $62.85   $62.90  
  Purchase #2 $177.36   13.161%   $200.7023   $200.70   $200.70   $200.70  
  Purchase #3 $165.63   11.267%   $184.2915   $184.29   $184.30   $184.30  
  Purchase #4 $198.85   11.506%   $221.7297   $221.73   $221.75   $221.70  
  Purchase #5 $36.36   10.795%   $40.2851   $40.29   $40.30   $40.30  
  Purchase #6 $155.62   13.139%   $176.0669   $176.07   $176.05   $176.10  
  Purchase #7 $69.62   7.309%   $74.7085   $74.71   $74.70   $74.70  
  7 purchase totals = $859.36       $960.6364   $960.64   $960.65   $960.70