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 $66.85   3.293%   $69.0514   $69.05   $69.05   $69.10  
  Purchase #2 $174.99   9.554%   $191.7085   $191.71   $191.70   $191.70  
  Purchase #3 $11.32   12.558%   $12.7416   $12.74   $12.75   $12.70  
  Purchase #4 $240.36   9.408%   $262.9731   $262.97   $262.95   $263.00  
  Purchase #5 $151.32   3.466%   $156.5648   $156.56   $156.55   $156.60  
  Purchase #6 $177.73   3.511%   $183.9701   $183.97   $183.95   $184.00  
  Purchase #7 $27.95   9.372%   $30.5695   $30.57   $30.55   $30.60  
  7 purchase totals = $850.52       $907.5790   $907.57   $907.50   $907.70