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 $209.31   6.798%   $223.5389   $223.54   $223.55   $223.50  
  Purchase #2 $69.63   8.542%   $75.5778   $75.58   $75.60   $75.60  
  Purchase #3 $117.84   13.790%   $134.0901   $134.09   $134.10   $134.10  
  Purchase #4 $176.61   10.153%   $194.5412   $194.54   $194.55   $194.50  
  Purchase #5 $234.90   13.584%   $266.8088   $266.81   $266.80   $266.80  
  Purchase #6 $9.77   8.663%   $10.6164   $10.62   $10.60   $10.60  
  Purchase #7 $169.63   13.578%   $192.6624   $192.66   $192.65   $192.70  
  7 purchase totals = $987.69       $1,097.8356   $1,097.84   $1,097.85   $1,097.80