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 $44.91   3.720%   $46.5807   $46.58   $46.60   $46.60  
  Purchase #2 $84.37   13.348%   $95.6317   $95.63   $95.65   $95.60  
  Purchase #3 $144.72   7.629%   $155.7607   $155.76   $155.75   $155.80  
  Purchase #4 $63.77   10.123%   $70.2254   $70.23   $70.25   $70.20  
  Purchase #5 $129.33   7.619%   $139.1837   $139.18   $139.20   $139.20  
  Purchase #6 $173.59   11.822%   $194.1118   $194.11   $194.10   $194.10  
  Purchase #7 $249.31   4.581%   $260.7309   $260.73   $260.75   $260.70  
  7 purchase totals = $890.00       $962.2249   $962.22   $962.30   $962.20