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 $192.44   6.485%   $204.9197   $204.92   $204.90   $204.90  
  Purchase #2 $83.31   3.211%   $85.9851   $85.99   $86.00   $86.00  
  Purchase #3 $55.25   3.230%   $57.0346   $57.03   $57.05   $57.00  
  Purchase #4 $60.58   11.551%   $67.5776   $67.58   $67.60   $67.60  
  Purchase #5 $158.61   13.121%   $179.4212   $179.42   $179.40   $179.40  
  Purchase #6 $122.83   9.327%   $134.2864   $134.29   $134.30   $134.30  
  Purchase #7 $42.38   4.209%   $44.1638   $44.16   $44.15   $44.20  
  7 purchase totals = $715.40       $773.3884   $773.39   $773.40   $773.40