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 $246.93   8.372%   $267.603   $267.60   $267.60   $267.60  
  Purchase #2 $142.43   8.478%   $154.5052   $154.51   $154.50   $154.50  
  Purchase #3 $238.32   4.320%   $248.6154   $248.62   $248.60   $248.60  
  Purchase #4 $99.37   5.189%   $104.5263   $104.53   $104.55   $104.50  
  Purchase #5 $163.81   6.457%   $174.3872   $174.39   $174.40   $174.40  
  Purchase #6 $32.82   13.547%   $37.2661   $37.27   $37.25   $37.30  
  Purchase #7 $199.36   9.732%   $218.7617   $218.76   $218.75   $218.80  
  7 purchase totals = $1,123.04       $1,205.6649   $1,205.68   $1,205.65   $1,205.70