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 $185.42   13.652%   $210.7335   $210.73   $210.75   $210.70  
  Purchase #2 $121.94   10.340%   $134.5486   $134.55   $134.55   $134.50  
  Purchase #3 $193.48   7.204%   $207.4183   $207.42   $207.40   $207.40  
  Purchase #4 $99.29   10.612%   $109.8267   $109.83   $109.85   $109.80  
  Purchase #5 $207.81   9.309%   $227.155   $227.16   $227.15   $227.20  
  Purchase #6 $62.67   10.792%   $69.4333   $69.43   $69.45   $69.40  
  Purchase #7 $223.32   8.193%   $241.6166   $241.62   $241.60   $241.60  
  7 purchase totals = $1,093.93       $1,200.7320   $1,200.74   $1,200.75   $1,200.60