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 $230.69   5.177%   $242.6328   $242.63   $242.65   $242.60  
  Purchase #2 $44.70   11.123%   $49.672   $49.67   $49.65   $49.70  
  Purchase #3 $49.43   4.140%   $51.4764   $51.48   $51.50   $51.50  
  Purchase #4 $128.86   5.158%   $135.5066   $135.51   $135.50   $135.50  
  Purchase #5 $157.91   5.443%   $166.505   $166.51   $166.50   $166.50  
  Purchase #6 $143.95   13.751%   $163.7446   $163.74   $163.75   $163.70  
  Purchase #7 $234.77   4.645%   $245.6751   $245.68   $245.70   $245.70  
  7 purchase totals = $990.31       $1,055.2125   $1,055.22   $1,055.25   $1,055.20