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 $237.71   11.604%   $265.2939   $265.29   $265.30   $265.30  
  Purchase #2 $248.91   7.809%   $268.3474   $268.35   $268.35   $268.30  
  Purchase #3 $54.90   3.687%   $56.9242   $56.92   $56.90   $56.90  
  Purchase #4 $153.38   5.655%   $162.0536   $162.05   $162.05   $162.10  
  Purchase #5 $30.45   11.718%   $34.0181   $34.02   $34.00   $34.00  
  Purchase #6 $50.38   9.419%   $55.1253   $55.13   $55.15   $55.10  
  Purchase #7 $185.75   12.126%   $208.274   $208.27   $208.25   $208.30  
  7 purchase totals = $961.48       $1,050.0365   $1,050.03   $1,050.00   $1,050.00