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 $243.83   10.608%   $269.6955   $269.70   $269.70   $269.70  
  Purchase #2 $31.73   3.545%   $32.8548   $32.85   $32.85   $32.90  
  Purchase #3 $7.91   5.208%   $8.322   $8.32   $8.30   $8.30  
  Purchase #4 $31.51   10.498%   $34.8179   $34.82   $34.80   $34.80  
  Purchase #5 $219.79   13.308%   $249.0397   $249.04   $249.05   $249.00  
  Purchase #6 $206.63   3.214%   $213.2711   $213.27   $213.25   $213.30  
  Purchase #7 $201.37   8.575%   $218.6375   $218.64   $218.65   $218.60  
  7 purchase totals = $942.77       $1,026.6385   $1,026.64   $1,026.60   $1,026.60