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 $184.58   12.170%   $207.0434   $207.04   $207.05   $207.00  
  Purchase #2 $128.97   10.441%   $142.4358   $142.44   $142.45   $142.40  
  Purchase #3 $168.99   8.606%   $183.5333   $183.53   $183.55   $183.50  
  Purchase #4 $188.45   3.742%   $195.5018   $195.50   $195.50   $195.50  
  Purchase #5 $113.36   6.102%   $120.2772   $120.28   $120.30   $120.30  
  Purchase #6 $113.70   3.378%   $117.5408   $117.54   $117.55   $117.50  
  Purchase #7 $116.29   12.741%   $131.1065   $131.11   $131.10   $131.10  
  7 purchase totals = $1,014.34       $1,097.4388   $1,097.44   $1,097.50   $1,097.30