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 $207.34   12.364%   $232.9755   $232.98   $233.00   $233.00  
  Purchase #2 $117.95   3.646%   $122.2505   $122.25   $122.25   $122.30  
  Purchase #3 $214.86   10.276%   $236.939   $236.94   $236.95   $236.90  
  Purchase #4 $237.64   10.669%   $262.9938   $262.99   $263.00   $263.00  
  Purchase #5 $221.27   12.144%   $248.141   $248.14   $248.15   $248.10  
  Purchase #6 $223.72   6.765%   $238.8547   $238.85   $238.85   $238.90  
  Purchase #7 $32.56   9.260%   $35.5751   $35.58   $35.60   $35.60  
  7 purchase totals = $1,255.34       $1,377.7296   $1,377.73   $1,377.80   $1,377.80