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 $59.89   8.536%   $65.0022   $65.00   $65.00   $65.00  
  Purchase #2 $114.98   8.386%   $124.6222   $124.62   $124.60   $124.60  
  Purchase #3 $232.66   6.731%   $248.3203   $248.32   $248.30   $248.30  
  Purchase #4 $14.82   7.323%   $15.9053   $15.91   $15.90   $15.90  
  Purchase #5 $157.53   6.434%   $167.6655   $167.67   $167.65   $167.70  
  Purchase #6 $188.78   6.708%   $201.4434   $201.44   $201.45   $201.40  
  Purchase #7 $221.69   12.674%   $249.787   $249.79   $249.80   $249.80  
  7 purchase totals = $990.35       $1,072.7459   $1,072.75   $1,072.70   $1,072.70