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 $26.71   10.549%   $29.5276   $29.53   $29.55   $29.50  
  Purchase #2 $163.79   3.551%   $169.6062   $169.61   $169.60   $169.60  
  Purchase #3 $224.71   10.448%   $248.1877   $248.19   $248.20   $248.20  
  Purchase #4 $174.43   8.252%   $188.824   $188.82   $188.80   $188.80  
  Purchase #5 $200.90   13.580%   $228.1822   $228.18   $228.20   $228.20  
  Purchase #6 $192.48   11.280%   $214.1917   $214.19   $214.20   $214.20  
  Purchase #7 $207.42   4.454%   $216.6585   $216.66   $216.65   $216.70  
  7 purchase totals = $1,190.44       $1,295.1779   $1,295.18   $1,295.20   $1,295.20