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 $183.65   13.624%   $208.6705   $208.67   $208.65   $208.70  
  Purchase #2 $18.65   4.140%   $19.4221   $19.42   $19.40   $19.40  
  Purchase #3 $23.96   6.670%   $25.5581   $25.56   $25.55   $25.60  
  Purchase #4 $82.31   12.813%   $92.8564   $92.86   $92.85   $92.90  
  Purchase #5 $228.58   13.365%   $259.1297   $259.13   $259.15   $259.10  
  Purchase #6 $195.68   9.601%   $214.4672   $214.47   $214.45   $214.50  
  Purchase #7 $46.32   7.308%   $49.7051   $49.71   $49.70   $49.70  
  7 purchase totals = $779.15       $869.8091   $869.82   $869.75   $869.90