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 $85.46   11.861%   $95.5964   $95.60   $95.60   $95.60  
  Purchase #2 $63.98   3.843%   $66.4388   $66.44   $66.45   $66.40  
  Purchase #3 $220.54   9.414%   $241.3016   $241.30   $241.30   $241.30  
  Purchase #4 $164.27   4.385%   $171.4732   $171.47   $171.45   $171.50  
  Purchase #5 $140.31   12.752%   $158.2023   $158.20   $158.20   $158.20  
  Purchase #6 $21.29   6.542%   $22.6828   $22.68   $22.70   $22.70  
  Purchase #7 $151.86   7.682%   $163.5259   $163.53   $163.55   $163.50  
  7 purchase totals = $847.71       $919.2210   $919.22   $919.25   $919.20