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 $181.59   12.872%   $204.9643   $204.96   $204.95   $205.00  
  Purchase #2 $100.94   13.484%   $114.5507   $114.55   $114.55   $114.60  
  Purchase #3 $234.78   12.337%   $263.7448   $263.74   $263.75   $263.70  
  Purchase #4 $51.46   12.236%   $57.7566   $57.76   $57.75   $57.80  
  Purchase #5 $224.96   5.233%   $236.7322   $236.73   $236.75   $236.70  
  Purchase #6 $240.84   4.825%   $252.4605   $252.46   $252.45   $252.50  
  Purchase #7 $85.36   7.141%   $91.4556   $91.46   $91.45   $91.50  
  7 purchase totals = $1,119.93       $1,221.6647   $1,221.66   $1,221.65   $1,221.80