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 $116.89   10.476%   $129.1354   $129.14   $129.15   $129.10  
  Purchase #2 $134.77   13.269%   $152.6526   $152.65   $152.65   $152.70  
  Purchase #3 $56.77   12.178%   $63.6835   $63.68   $63.70   $63.70  
  Purchase #4 $233.44   6.578%   $248.7957   $248.80   $248.80   $248.80  
  Purchase #5 $116.93   6.542%   $124.5796   $124.58   $124.60   $124.60  
  Purchase #6 $48.91   9.476%   $53.5447   $53.54   $53.55   $53.50  
  Purchase #7 $167.68   6.477%   $178.5406   $178.54   $178.55   $178.50  
  7 purchase totals = $875.39       $950.9321   $950.93   $951.00   $950.90