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 $239.40   6.291%   $254.4607   $254.46   $254.45   $254.50  
  Purchase #2 $42.26   13.352%   $47.9026   $47.90   $47.90   $47.90  
  Purchase #3 $73.50   7.501%   $79.0132   $79.01   $79.00   $79.00  
  Purchase #4 $74.94   8.219%   $81.0993   $81.10   $81.10   $81.10  
  Purchase #5 $206.31   3.437%   $213.4009   $213.40   $213.40   $213.40  
  Purchase #6 $199.71   13.373%   $226.4172   $226.42   $226.40   $226.40  
  Purchase #7 $58.57   5.346%   $61.7012   $61.70   $61.70   $61.70  
  7 purchase totals = $894.69       $963.9951   $963.99   $963.95   $964.00