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 $224.46   11.291%   $249.8038   $249.80   $249.80   $249.80  
  Purchase #2 $86.74   8.493%   $94.1068   $94.11   $94.10   $94.10  
  Purchase #3 $211.63   5.719%   $223.7331   $223.73   $223.75   $223.70  
  Purchase #4 $88.53   9.836%   $97.2378   $97.24   $97.25   $97.20  
  Purchase #5 $240.89   9.484%   $263.736   $263.74   $263.75   $263.70  
  Purchase #6 $170.48   8.286%   $184.606   $184.61   $184.60   $184.60  
  Purchase #7 $92.25   3.722%   $95.6835   $95.68   $95.70   $95.70  
  7 purchase totals = $1,114.98       $1,208.9070   $1,208.91   $1,208.95   $1,208.80