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 $104.91   9.405%   $114.7768   $114.78   $114.80   $114.80  
  Purchase #2 $61.58   11.464%   $68.6395   $68.64   $68.65   $68.60  
  Purchase #3 $53.83   8.675%   $58.4998   $58.50   $58.50   $58.50  
  Purchase #4 $30.35   11.550%   $33.8554   $33.86   $33.85   $33.90  
  Purchase #5 $88.52   10.640%   $97.9385   $97.94   $97.95   $97.90  
  Purchase #6 $195.60   5.821%   $206.9859   $206.99   $207.00   $207.00  
  Purchase #7 $238.63   9.439%   $261.1543   $261.15   $261.15   $261.20  
  7 purchase totals = $773.42       $841.8502   $841.86   $841.90   $841.90