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 $203.74   11.192%   $226.5426   $226.54   $226.55   $226.50  
  Purchase #2 $13.76   10.845%   $15.2523   $15.25   $15.25   $15.30  
  Purchase #3 $239.34   6.167%   $254.1001   $254.10   $254.10   $254.10  
  Purchase #4 $182.84   10.249%   $201.5793   $201.58   $201.60   $201.60  
  Purchase #5 $154.28   12.326%   $173.2966   $173.30   $173.30   $173.30  
  Purchase #6 $158.72   4.387%   $165.683   $165.68   $165.70   $165.70  
  Purchase #7 $169.25   6.597%   $180.4154   $180.42   $180.40   $180.40  
  7 purchase totals = $1,121.93       $1,216.8693   $1,216.87   $1,216.90   $1,216.90