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 $182.91   13.206%   $207.0651   $207.07   $207.05   $207.10  
  Purchase #2 $165.41   7.799%   $178.3103   $178.31   $178.30   $178.30  
  Purchase #3 $66.70   3.626%   $69.1185   $69.12   $69.10   $69.10  
  Purchase #4 $77.58   7.758%   $83.5987   $83.60   $83.60   $83.60  
  Purchase #5 $219.88   10.141%   $242.178   $242.18   $242.20   $242.20  
  Purchase #6 $162.71   9.341%   $177.9087   $177.91   $177.90   $177.90  
  Purchase #7 $208.72   11.288%   $232.2803   $232.28   $232.30   $232.30  
  7 purchase totals = $1,083.91       $1,190.4596   $1,190.47   $1,190.45   $1,190.50