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 $36.61   12.604%   $41.2243   $41.22   $41.20   $41.20  
  Purchase #2 $79.37   11.584%   $88.5642   $88.56   $88.55   $88.60  
  Purchase #3 $163.89   7.856%   $176.7652   $176.77   $176.75   $176.80  
  Purchase #4 $202.46   3.357%   $209.2566   $209.26   $209.25   $209.30  
  Purchase #5 $174.96   6.794%   $186.8468   $186.85   $186.85   $186.80  
  Purchase #6 $119.57   12.575%   $134.6059   $134.61   $134.60   $134.60  
  Purchase #7 $26.49   7.832%   $28.5647   $28.56   $28.55   $28.60  
  7 purchase totals = $803.35       $865.8277   $865.83   $865.75   $865.90