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 $245.53   7.658%   $264.3327   $264.33   $264.35   $264.30  
  Purchase #2 $229.60   8.423%   $248.9392   $248.94   $248.95   $248.90  
  Purchase #3 $101.43   11.537%   $113.132   $113.13   $113.15   $113.10  
  Purchase #4 $235.90   5.783%   $249.5421   $249.54   $249.55   $249.50  
  Purchase #5 $229.90   4.735%   $240.7858   $240.79   $240.80   $240.80  
  Purchase #6 $77.99   4.383%   $81.4083   $81.41   $81.40   $81.40  
  Purchase #7 $224.37   5.745%   $237.2601   $237.26   $237.25   $237.30  
  7 purchase totals = $1,344.72       $1,435.4002   $1,435.40   $1,435.45   $1,435.30