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 $218.59   8.752%   $237.721   $237.72   $237.70   $237.70  
  Purchase #2 $108.57   8.386%   $117.6747   $117.67   $117.65   $117.70  
  Purchase #3 $159.93   4.136%   $166.5447   $166.54   $166.55   $166.50  
  Purchase #4 $172.88   6.261%   $183.704   $183.70   $183.70   $183.70  
  Purchase #5 $76.93   11.725%   $85.95   $85.95   $85.95   $86.00  
  Purchase #6 $56.36   12.252%   $63.2652   $63.27   $63.25   $63.30  
  Purchase #7 $140.49   11.331%   $156.4089   $156.41   $156.40   $156.40  
  7 purchase totals = $933.75       $1,011.2685   $1,011.26   $1,011.20   $1,011.30