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 $219.90   8.508%   $238.6091   $238.61   $238.60   $238.60  
  Purchase #2 $208.91   8.277%   $226.2015   $226.20   $226.20   $226.20  
  Purchase #3 $151.77   11.834%   $169.7305   $169.73   $169.75   $169.70  
  Purchase #4 $245.69   9.578%   $269.2222   $269.22   $269.20   $269.20  
  Purchase #5 $146.61   3.740%   $152.0932   $152.09   $152.10   $152.10  
  Purchase #6 $43.61   9.338%   $47.6823   $47.68   $47.70   $47.70  
  Purchase #7 $217.46   11.401%   $242.2526   $242.25   $242.25   $242.30  
  7 purchase totals = $1,233.95       $1,345.7914   $1,345.78   $1,345.80   $1,345.80