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 $211.41   13.187%   $239.2886   $239.29   $239.30   $239.30  
  Purchase #2 $60.35   3.156%   $62.2546   $62.25   $62.25   $62.30  
  Purchase #3 $86.57   4.554%   $90.5124   $90.51   $90.50   $90.50  
  Purchase #4 $66.95   3.204%   $69.0951   $69.10   $69.10   $69.10  
  Purchase #5 $85.68   3.658%   $88.8142   $88.81   $88.80   $88.80  
  Purchase #6 $177.93   8.417%   $192.9064   $192.91   $192.90   $192.90  
  Purchase #7 $237.53   7.314%   $254.9029   $254.90   $254.90   $254.90  
  7 purchase totals = $926.42       $997.7742   $997.77   $997.75   $997.80