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 $86.74   8.265%   $93.9091   $93.91   $93.90   $93.90  
  Purchase #2 $198.31   10.102%   $218.3433   $218.34   $218.35   $218.30  
  Purchase #3 $43.44   8.479%   $47.1233   $47.12   $47.10   $47.10  
  Purchase #4 $32.71   4.327%   $34.1254   $34.13   $34.15   $34.10  
  Purchase #5 $237.58   10.799%   $263.2363   $263.24   $263.25   $263.20  
  Purchase #6 $250.62   12.749%   $282.5715   $282.57   $282.55   $282.60  
  Purchase #7 $100.64   13.521%   $114.2475   $114.25   $114.25   $114.20  
  7 purchase totals = $950.04       $1,053.5564   $1,053.56   $1,053.55   $1,053.40