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 $169.60   8.312%   $183.6972   $183.70   $183.70   $183.70  
  Purchase #2 $170.97   13.455%   $193.974   $193.97   $193.95   $194.00  
  Purchase #3 $189.46   13.618%   $215.2607   $215.26   $215.25   $215.30  
  Purchase #4 $163.44   13.429%   $185.3884   $185.39   $185.40   $185.40  
  Purchase #5 $165.37   3.771%   $171.6061   $171.61   $171.60   $171.60  
  Purchase #6 $227.65   4.293%   $237.423   $237.42   $237.40   $237.40  
  Purchase #7 $89.77   8.808%   $97.6769   $97.68   $97.70   $97.70  
  7 purchase totals = $1,176.26       $1,285.0263   $1,285.03   $1,285.00   $1,285.10