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 $84.27   9.470%   $92.2504   $92.25   $92.25   $92.30  
  Purchase #2 $186.69   8.439%   $202.4448   $202.44   $202.45   $202.40  
  Purchase #3 $143.32   7.699%   $154.3542   $154.35   $154.35   $154.40  
  Purchase #4 $164.49   12.632%   $185.2684   $185.27   $185.25   $185.30  
  Purchase #5 $148.40   5.747%   $156.9285   $156.93   $156.95   $156.90  
  Purchase #6 $13.33   5.109%   $14.011   $14.01   $14.00   $14.00  
  Purchase #7 $114.75   11.189%   $127.5894   $127.59   $127.60   $127.60  
  7 purchase totals = $855.25       $932.8467   $932.84   $932.85   $932.90