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 $250.26   10.627%   $276.8551   $276.86   $276.85   $276.90  
  Purchase #2 $182.97   12.344%   $205.5558   $205.56   $205.55   $205.60  
  Purchase #3 $22.62   10.751%   $25.0519   $25.05   $25.05   $25.10  
  Purchase #4 $114.41   11.729%   $127.8291   $127.83   $127.85   $127.80  
  Purchase #5 $57.40   5.590%   $60.6087   $60.61   $60.60   $60.60  
  Purchase #6 $201.53   11.544%   $224.7946   $224.79   $224.80   $224.80  
  Purchase #7 $97.31   10.665%   $107.6881   $107.69   $107.70   $107.70  
  7 purchase totals = $926.50       $1,028.3833   $1,028.39   $1,028.40   $1,028.50