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 $167.97   9.457%   $183.8549   $183.85   $183.85   $183.90  
  Purchase #2 $247.46   13.732%   $281.4412   $281.44   $281.45   $281.40  
  Purchase #3 $233.82   6.314%   $248.5834   $248.58   $248.60   $248.60  
  Purchase #4 $55.67   3.261%   $57.4854   $57.49   $57.50   $57.50  
  Purchase #5 $104.59   10.668%   $115.7477   $115.75   $115.75   $115.70  
  Purchase #6 $112.39   4.464%   $117.4071   $117.41   $117.40   $117.40  
  Purchase #7 $183.44   10.217%   $202.1821   $202.18   $202.20   $202.20  
  7 purchase totals = $1,105.34       $1,206.7018   $1,206.70   $1,206.75   $1,206.70