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 $216.27   8.747%   $235.1871   $235.19   $235.20   $235.20  
  Purchase #2 $235.29   13.793%   $267.7435   $267.74   $267.75   $267.70  
  Purchase #3 $63.65   3.607%   $65.9459   $65.95   $65.95   $65.90  
  Purchase #4 $88.74   6.437%   $94.4522   $94.45   $94.45   $94.50  
  Purchase #5 $8.90   4.129%   $9.2675   $9.27   $9.25   $9.30  
  Purchase #6 $102.30   12.113%   $114.6916   $114.69   $114.70   $114.70  
  Purchase #7 $51.99   10.179%   $57.2821   $57.28   $57.30   $57.30  
  7 purchase totals = $767.14       $844.5699   $844.57   $844.60   $844.60