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 $54.48   6.299%   $57.9117   $57.91   $57.90   $57.90  
  Purchase #2 $57.87   3.646%   $59.9799   $59.98   $60.00   $60.00  
  Purchase #3 $245.30   5.341%   $258.4015   $258.40   $258.40   $258.40  
  Purchase #4 $226.65   4.857%   $237.6584   $237.66   $237.65   $237.70  
  Purchase #5 $171.54   5.188%   $180.4395   $180.44   $180.45   $180.40  
  Purchase #6 $131.91   3.542%   $136.5823   $136.58   $136.60   $136.60  
  Purchase #7 $213.47   7.571%   $229.6318   $229.63   $229.65   $229.60  
  7 purchase totals = $1,101.22       $1,160.6051   $1,160.60   $1,160.65   $1,160.60