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 $39.74   11.478%   $44.3014   $44.30   $44.30   $44.30  
  Purchase #2 $62.98   10.270%   $69.448   $69.45   $69.45   $69.40  
  Purchase #3 $249.79   11.467%   $278.4334   $278.43   $278.45   $278.40  
  Purchase #4 $67.28   9.109%   $73.4085   $73.41   $73.40   $73.40  
  Purchase #5 $50.77   6.579%   $54.1102   $54.11   $54.10   $54.10  
  Purchase #6 $164.83   12.369%   $185.2178   $185.22   $185.20   $185.20  
  Purchase #7 $214.93   6.293%   $228.4555   $228.46   $228.45   $228.50  
  7 purchase totals = $850.32       $933.3748   $933.38   $933.35   $933.30