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 $196.57   4.591%   $205.5945   $205.59   $205.60   $205.60  
  Purchase #2 $114.30   6.678%   $121.933   $121.93   $121.95   $121.90  
  Purchase #3 $102.58   4.372%   $107.0648   $107.06   $107.05   $107.10  
  Purchase #4 $232.38   12.548%   $261.539   $261.54   $261.55   $261.50  
  Purchase #5 $169.98   13.456%   $192.8525   $192.85   $192.85   $192.90  
  Purchase #6 $200.88   6.476%   $213.889   $213.89   $213.90   $213.90  
  Purchase #7 $177.80   7.547%   $191.2186   $191.22   $191.20   $191.20  
  7 purchase totals = $1,194.49       $1,294.0914   $1,294.08   $1,294.10   $1,294.10