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 $54.48   10.588%   $60.2483   $60.25   $60.25   $60.20  
  Purchase #2 $98.77   10.496%   $109.1369   $109.14   $109.15   $109.10  
  Purchase #3 $113.67   5.217%   $119.6002   $119.60   $119.60   $119.60  
  Purchase #4 $198.26   13.328%   $224.6841   $224.68   $224.70   $224.70  
  Purchase #5 $112.65   7.129%   $120.6808   $120.68   $120.70   $120.70  
  Purchase #6 $157.99   4.161%   $164.564   $164.56   $164.55   $164.60  
  Purchase #7 $5.71   5.172%   $6.0053   $6.01   $6.00   $6.00  
  7 purchase totals = $741.53       $804.9196   $804.92   $804.95   $804.90