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 $60.74   8.155%   $65.6933   $65.69   $65.70   $65.70  
  Purchase #2 $79.25   7.223%   $84.9742   $84.97   $84.95   $85.00  
  Purchase #3 $179.60   8.372%   $194.6361   $194.64   $194.65   $194.60  
  Purchase #4 $112.91   12.623%   $127.1626   $127.16   $127.15   $127.20  
  Purchase #5 $206.28   7.697%   $222.1574   $222.16   $222.15   $222.20  
  Purchase #6 $185.72   12.378%   $208.7084   $208.71   $208.70   $208.70  
  Purchase #7 $250.76   7.239%   $268.9125   $268.91   $268.90   $268.90  
  7 purchase totals = $1,075.26       $1,172.2445   $1,172.24   $1,172.20   $1,172.30