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 $92.57   6.498%   $98.5852   $98.59   $98.60   $98.60  
  Purchase #2 $59.53   6.399%   $63.3393   $63.34   $63.35   $63.30  
  Purchase #3 $134.71   6.481%   $143.4406   $143.44   $143.45   $143.40  
  Purchase #4 $39.54   9.564%   $43.3216   $43.32   $43.30   $43.30  
  Purchase #5 $107.74   6.300%   $114.5276   $114.53   $114.55   $114.50  
  Purchase #6 $53.96   5.608%   $56.9861   $56.99   $57.00   $57.00  
  Purchase #7 $228.98   9.495%   $250.7217   $250.72   $250.70   $250.70  
  7 purchase totals = $717.03       $770.9221   $770.93   $770.95   $770.80