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 $130.44   10.159%   $143.6914   $143.69   $143.70   $143.70  
  Purchase #2 $112.63   6.228%   $119.6446   $119.64   $119.65   $119.60  
  Purchase #3 $164.72   11.317%   $183.3614   $183.36   $183.35   $183.40  
  Purchase #4 $159.28   10.827%   $176.5252   $176.53   $176.55   $176.50  
  Purchase #5 $49.53   8.375%   $53.6781   $53.68   $53.70   $53.70  
  Purchase #6 $94.99   13.397%   $107.7158   $107.72   $107.70   $107.70  
  Purchase #7 $59.43   6.108%   $63.06   $63.06   $63.05   $63.10  
  7 purchase totals = $771.02       $847.6765   $847.68   $847.70   $847.70