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 $248.85   10.666%   $275.3923   $275.39   $275.40   $275.40  
  Purchase #2 $65.29   6.597%   $69.5972   $69.60   $69.60   $69.60  
  Purchase #3 $162.34   8.807%   $176.6373   $176.64   $176.65   $176.60  
  Purchase #4 $51.70   6.449%   $55.0341   $55.03   $55.05   $55.00  
  Purchase #5 $222.65   6.378%   $236.8506   $236.85   $236.85   $236.90  
  Purchase #6 $119.92   6.383%   $127.5745   $127.57   $127.55   $127.60  
  Purchase #7 $91.65   3.555%   $94.9082   $94.91   $94.90   $94.90  
  7 purchase totals = $962.40       $1,035.9942   $1,035.99   $1,036.00   $1,036.00