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 $184.85   3.737%   $191.7578   $191.76   $191.75   $191.80  
  Purchase #2 $46.70   10.647%   $51.6721   $51.67   $51.65   $51.70  
  Purchase #3 $112.43   11.738%   $125.627   $125.63   $125.65   $125.60  
  Purchase #4 $240.81   3.204%   $248.5256   $248.53   $248.55   $248.50  
  Purchase #5 $218.34   9.656%   $239.4229   $239.42   $239.40   $239.40  
  Purchase #6 $166.92   11.270%   $185.7319   $185.73   $185.75   $185.70  
  Purchase #7 $81.49   4.502%   $85.1587   $85.16   $85.15   $85.20  
  7 purchase totals = $1,051.54       $1,127.8960   $1,127.90   $1,127.90   $1,127.90