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 $54.82   12.443%   $61.6413   $61.64   $61.65   $61.60  
  Purchase #2 $172.55   10.246%   $190.2295   $190.23   $190.25   $190.20  
  Purchase #3 $162.68   11.821%   $181.9104   $181.91   $181.90   $181.90  
  Purchase #4 $136.42   13.129%   $154.3306   $154.33   $154.35   $154.30  
  Purchase #5 $119.97   13.226%   $135.8372   $135.84   $135.85   $135.80  
  Purchase #6 $232.46   13.214%   $263.1773   $263.18   $263.20   $263.20  
  Purchase #7 $103.25   10.443%   $114.0324   $114.03   $114.05   $114.00  
  7 purchase totals = $982.15       $1,101.1587   $1,101.16   $1,101.25   $1,101.00