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 $49.57   11.751%   $55.395   $55.40   $55.40   $55.40  
  Purchase #2 $173.96   10.762%   $192.6816   $192.68   $192.70   $192.70  
  Purchase #3 $97.36   13.762%   $110.7587   $110.76   $110.75   $110.80  
  Purchase #4 $246.36   3.326%   $254.5539   $254.55   $254.55   $254.60  
  Purchase #5 $10.76   4.786%   $11.275   $11.28   $11.30   $11.30  
  Purchase #6 $165.37   5.397%   $174.295   $174.30   $174.30   $174.30  
  Purchase #7 $222.62   13.321%   $252.2752   $252.28   $252.30   $252.30  
  7 purchase totals = $966.00       $1,051.2344   $1,051.25   $1,051.30   $1,051.40