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 $196.88   12.281%   $221.0588   $221.06   $221.05   $221.10  
  Purchase #2 $55.71   4.739%   $58.3501   $58.35   $58.35   $58.40  
  Purchase #3 $35.94   6.507%   $38.2786   $38.28   $38.30   $38.30  
  Purchase #4 $43.98   8.683%   $47.7988   $47.80   $47.80   $47.80  
  Purchase #5 $198.55   7.232%   $212.9091   $212.91   $212.90   $212.90  
  Purchase #6 $30.88   10.275%   $34.0529   $34.05   $34.05   $34.10  
  Purchase #7 $154.74   4.392%   $161.5362   $161.54   $161.55   $161.50  
  7 purchase totals = $716.68       $773.9845   $773.99   $774.00   $774.10