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 $244.55   11.655%   $273.0523   $273.05   $273.05   $273.10  
  Purchase #2 $128.38   13.733%   $146.0104   $146.01   $146.00   $146.00  
  Purchase #3 $185.70   12.121%   $208.2087   $208.21   $208.20   $208.20  
  Purchase #4 $202.68   8.843%   $220.603   $220.60   $220.60   $220.60  
  Purchase #5 $205.46   4.585%   $214.8803   $214.88   $214.90   $214.90  
  Purchase #6 $50.92   10.398%   $56.2147   $56.21   $56.20   $56.20  
  Purchase #7 $77.92   8.555%   $84.5861   $84.59   $84.60   $84.60  
  7 purchase totals = $1,095.61       $1,203.5555   $1,203.55   $1,203.55   $1,203.60