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 $79.63   8.696%   $86.5546   $86.55   $86.55   $86.60  
  Purchase #2 $110.26   13.426%   $125.0635   $125.06   $125.05   $125.10  
  Purchase #3 $15.53   9.472%   $17.001   $17.00   $17.00   $17.00  
  Purchase #4 $49.81   13.613%   $56.5906   $56.59   $56.60   $56.60  
  Purchase #5 $227.55   7.171%   $243.8676   $243.87   $243.85   $243.90  
  Purchase #6 $60.31   8.478%   $65.4231   $65.42   $65.40   $65.40  
  Purchase #7 $237.63   5.114%   $249.7824   $249.78   $249.80   $249.80  
  7 purchase totals = $780.72       $844.2828   $844.27   $844.25   $844.40