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 $248.87   7.302%   $267.0425   $267.04   $267.05   $267.00  
  Purchase #2 $60.86   9.186%   $66.4506   $66.45   $66.45   $66.50  
  Purchase #3 $32.74   4.837%   $34.3236   $34.32   $34.30   $34.30  
  Purchase #4 $213.62   6.693%   $227.9176   $227.92   $227.90   $227.90  
  Purchase #5 $191.55   4.851%   $200.8421   $200.84   $200.85   $200.80  
  Purchase #6 $154.40   11.201%   $171.6943   $171.69   $171.70   $171.70  
  Purchase #7 $120.43   8.495%   $130.6605   $130.66   $130.65   $130.70  
  7 purchase totals = $1,022.47       $1,098.9312   $1,098.92   $1,098.90   $1,098.90