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 $244.91   8.522%   $265.7812   $265.78   $265.80   $265.80  
  Purchase #2 $38.81   6.861%   $41.4728   $41.47   $41.45   $41.50  
  Purchase #3 $151.25   13.691%   $171.9576   $171.96   $171.95   $172.00  
  Purchase #4 $218.92   9.320%   $239.3233   $239.32   $239.30   $239.30  
  Purchase #5 $44.29   8.510%   $48.0591   $48.06   $48.05   $48.10  
  Purchase #6 $238.39   8.804%   $259.3779   $259.38   $259.40   $259.40  
  Purchase #7 $24.41   7.103%   $26.1438   $26.14   $26.15   $26.10  
  7 purchase totals = $960.98       $1,052.1157   $1,052.11   $1,052.10   $1,052.20