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 $168.90   11.135%   $187.707   $187.71   $187.70   $187.70  
  Purchase #2 $116.49   7.315%   $125.0112   $125.01   $125.00   $125.00  
  Purchase #3 $69.82   6.762%   $74.5412   $74.54   $74.55   $74.50  
  Purchase #4 $195.61   8.144%   $211.5405   $211.54   $211.55   $211.50  
  Purchase #5 $227.93   13.636%   $259.0105   $259.01   $259.00   $259.00  
  Purchase #6 $169.66   13.536%   $192.6252   $192.63   $192.65   $192.60  
  Purchase #7 $78.83   13.596%   $89.5477   $89.55   $89.55   $89.50  
  7 purchase totals = $1,027.24       $1,139.9833   $1,139.99   $1,140.00   $1,139.80