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 $92.25   12.543%   $103.8209   $103.82   $103.80   $103.80  
  Purchase #2 $124.95   8.482%   $135.5483   $135.55   $135.55   $135.50  
  Purchase #3 $112.73   8.518%   $122.3323   $122.33   $122.35   $122.30  
  Purchase #4 $95.82   11.729%   $107.0587   $107.06   $107.05   $107.10  
  Purchase #5 $239.33   6.105%   $253.9411   $253.94   $253.95   $253.90  
  Purchase #6 $184.33   7.425%   $198.0165   $198.02   $198.00   $198.00  
  Purchase #7 $223.36   11.302%   $248.6041   $248.60   $248.60   $248.60  
  7 purchase totals = $1,072.77       $1,169.3219   $1,169.32   $1,169.30   $1,169.20