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 $206.26   13.793%   $234.7094   $234.71   $234.70   $234.70  
  Purchase #2 $240.51   13.843%   $273.8038   $273.80   $273.80   $273.80  
  Purchase #3 $137.48   12.185%   $154.2319   $154.23   $154.25   $154.20  
  Purchase #4 $162.40   11.237%   $180.6489   $180.65   $180.65   $180.60  
  Purchase #5 $32.61   6.708%   $34.7975   $34.80   $34.80   $34.80  
  Purchase #6 $114.54   11.452%   $127.6571   $127.66   $127.65   $127.70  
  Purchase #7 $110.43   7.528%   $118.7432   $118.74   $118.75   $118.70  
  7 purchase totals = $1,004.23       $1,124.5918   $1,124.59   $1,124.60   $1,124.50