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 $246.56   12.274%   $276.8228   $276.82   $276.80   $276.80  
  Purchase #2 $201.66   5.353%   $212.4549   $212.45   $212.45   $212.50  
  Purchase #3 $114.78   8.513%   $124.5512   $124.55   $124.55   $124.60  
  Purchase #4 $194.73   5.402%   $205.2493   $205.25   $205.25   $205.20  
  Purchase #5 $124.83   7.767%   $134.5255   $134.53   $134.55   $134.50  
  Purchase #6 $203.81   11.628%   $227.509   $227.51   $227.50   $227.50  
  Purchase #7 $82.78   4.534%   $86.5332   $86.53   $86.55   $86.50  
  7 purchase totals = $1,169.15       $1,267.6459   $1,267.64   $1,267.65   $1,267.60