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 $237.51   13.589%   $269.7852   $269.79   $269.80   $269.80  
  Purchase #2 $53.86   6.590%   $57.4094   $57.41   $57.40   $57.40  
  Purchase #3 $219.53   7.718%   $236.4733   $236.47   $236.45   $236.50  
  Purchase #4 $213.33   3.362%   $220.5022   $220.50   $220.50   $220.50  
  Purchase #5 $125.77   11.816%   $140.631   $140.63   $140.65   $140.60  
  Purchase #6 $119.43   11.610%   $133.2958   $133.30   $133.30   $133.30  
  Purchase #7 $13.48   3.175%   $13.908   $13.91   $13.90   $13.90  
  7 purchase totals = $982.91       $1,072.0049   $1,072.01   $1,072.00   $1,072.00