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 $86.63   12.542%   $97.4951   $97.50   $97.50   $97.50  
  Purchase #2 $163.65   10.206%   $180.3521   $180.35   $180.35   $180.40  
  Purchase #3 $127.27   8.159%   $137.654   $137.65   $137.65   $137.70  
  Purchase #4 $129.44   8.757%   $140.7751   $140.78   $140.80   $140.80  
  Purchase #5 $43.78   11.693%   $48.8992   $48.90   $48.90   $48.90  
  Purchase #6 $223.61   5.482%   $235.8683   $235.87   $235.85   $235.90  
  Purchase #7 $119.77   11.536%   $133.5867   $133.59   $133.60   $133.60  
  7 purchase totals = $894.15       $974.6305   $974.64   $974.65   $974.80