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 $248.63   4.304%   $259.331   $259.33   $259.35   $259.30  
  Purchase #2 $12.81   9.436%   $14.0188   $14.02   $14.00   $14.00  
  Purchase #3 $46.56   4.787%   $48.7888   $48.79   $48.80   $48.80  
  Purchase #4 $62.29   11.534%   $69.4745   $69.47   $69.45   $69.50  
  Purchase #5 $236.63   4.226%   $246.63   $246.63   $246.65   $246.60  
  Purchase #6 $174.60   12.386%   $196.226   $196.23   $196.25   $196.20  
  Purchase #7 $157.51   9.129%   $171.8891   $171.89   $171.90   $171.90  
  7 purchase totals = $939.03       $1,006.3582   $1,006.36   $1,006.40   $1,006.30