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 $179.61   6.754%   $191.7409   $191.74   $191.75   $191.70  
  Purchase #2 $66.99   6.665%   $71.4549   $71.45   $71.45   $71.50  
  Purchase #3 $159.67   8.437%   $173.1414   $173.14   $173.15   $173.10  
  Purchase #4 $175.82   13.869%   $200.2045   $200.20   $200.20   $200.20  
  Purchase #5 $63.83   10.823%   $70.7383   $70.74   $70.75   $70.70  
  Purchase #6 $167.93   13.777%   $191.0657   $191.07   $191.05   $191.10  
  Purchase #7 $170.83   3.544%   $176.8842   $176.88   $176.90   $176.90  
  7 purchase totals = $984.68       $1,075.2299   $1,075.22   $1,075.25   $1,075.20