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 $159.46   11.814%   $178.2986   $178.30   $178.30   $178.30  
  Purchase #2 $196.38   12.563%   $221.0512   $221.05   $221.05   $221.10  
  Purchase #3 $75.99   11.607%   $84.8102   $84.81   $84.80   $84.80  
  Purchase #4 $209.77   6.171%   $222.7149   $222.71   $222.70   $222.70  
  Purchase #5 $226.82   8.284%   $245.6098   $245.61   $245.60   $245.60  
  Purchase #6 $250.87   4.717%   $262.7035   $262.70   $262.70   $262.70  
  Purchase #7 $41.44   8.324%   $44.8895   $44.89   $44.90   $44.90  
  7 purchase totals = $1,160.73       $1,260.0777   $1,260.07   $1,260.05   $1,260.10