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 $38.68   12.471%   $43.5038   $43.50   $43.50   $43.50  
  Purchase #2 $233.58   5.407%   $246.2097   $246.21   $246.20   $246.20  
  Purchase #3 $49.43   10.752%   $54.7447   $54.74   $54.75   $54.70  
  Purchase #4 $190.97   7.460%   $205.2164   $205.22   $205.20   $205.20  
  Purchase #5 $22.86   10.618%   $25.2873   $25.29   $25.30   $25.30  
  Purchase #6 $186.88   3.382%   $193.2003   $193.20   $193.20   $193.20  
  Purchase #7 $106.92   12.171%   $119.9332   $119.93   $119.95   $119.90  
  7 purchase totals = $829.32       $888.0954   $888.09   $888.10   $888.00