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 $113.67   8.263%   $123.0626   $123.06   $123.05   $123.10  
  Purchase #2 $250.88   6.691%   $267.6664   $267.67   $267.65   $267.70  
  Purchase #3 $14.65   11.648%   $16.3564   $16.36   $16.35   $16.40  
  Purchase #4 $50.37   3.792%   $52.28   $52.28   $52.30   $52.30  
  Purchase #5 $199.70   12.437%   $224.5367   $224.54   $224.55   $224.50  
  Purchase #6 $108.99   13.280%   $123.4639   $123.46   $123.45   $123.50  
  Purchase #7 $219.63   13.118%   $248.4411   $248.44   $248.45   $248.40  
  7 purchase totals = $957.89       $1,055.8071   $1,055.81   $1,055.80   $1,055.90