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 $240.98   11.602%   $268.9385   $268.94   $268.95   $268.90  
  Purchase #2 $240.80   13.239%   $272.6795   $272.68   $272.70   $272.70  
  Purchase #3 $41.84   3.242%   $43.1965   $43.20   $43.20   $43.20  
  Purchase #4 $171.57   12.238%   $192.5667   $192.57   $192.55   $192.60  
  Purchase #5 $207.76   13.745%   $236.3166   $236.32   $236.30   $236.30  
  Purchase #6 $148.52   9.605%   $162.7853   $162.79   $162.80   $162.80  
  Purchase #7 $244.45   7.498%   $262.7789   $262.78   $262.80   $262.80  
  7 purchase totals = $1,295.92       $1,439.2620   $1,439.28   $1,439.30   $1,439.30