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 $241.38   8.302%   $261.4194   $261.42   $261.40   $261.40  
  Purchase #2 $174.91   11.223%   $194.5401   $194.54   $194.55   $194.50  
  Purchase #3 $48.86   7.782%   $52.6623   $52.66   $52.65   $52.70  
  Purchase #4 $211.81   12.183%   $237.6148   $237.61   $237.60   $237.60  
  Purchase #5 $157.87   4.555%   $165.061   $165.06   $165.05   $165.10  
  Purchase #6 $134.57   13.323%   $152.4988   $152.50   $152.50   $152.50  
  Purchase #7 $202.89   9.247%   $221.6512   $221.65   $221.65   $221.70  
  7 purchase totals = $1,172.29       $1,285.4476   $1,285.44   $1,285.40   $1,285.50