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 $32.44   7.153%   $34.7604   $34.76   $34.75   $34.80  
  Purchase #2 $225.31   11.163%   $250.4614   $250.46   $250.45   $250.50  
  Purchase #3 $15.75   4.468%   $16.4537   $16.45   $16.45   $16.50  
  Purchase #4 $214.91   11.445%   $239.5064   $239.51   $239.50   $239.50  
  Purchase #5 $135.32   8.187%   $146.3986   $146.40   $146.40   $146.40  
  Purchase #6 $152.40   12.377%   $171.2625   $171.26   $171.25   $171.30  
  Purchase #7 $185.54   13.762%   $211.074   $211.07   $211.05   $211.10  
  7 purchase totals = $961.67       $1,069.9170   $1,069.91   $1,069.85   $1,070.10