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 $107.25   10.574%   $118.5906   $118.59   $118.60   $118.60  
  Purchase #2 $66.53   4.786%   $69.7141   $69.71   $69.70   $69.70  
  Purchase #3 $61.31   11.320%   $68.2503   $68.25   $68.25   $68.30  
  Purchase #4 $163.52   5.286%   $172.1637   $172.16   $172.15   $172.20  
  Purchase #5 $184.26   11.627%   $205.6839   $205.68   $205.70   $205.70  
  Purchase #6 $98.74   13.669%   $112.2368   $112.24   $112.25   $112.20  
  Purchase #7 $31.63   4.327%   $32.9986   $33.00   $33.00   $33.00  
  7 purchase totals = $713.24       $779.6380   $779.63   $779.65   $779.70