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 $202.49   6.452%   $215.5547   $215.55   $215.55   $215.60  
  Purchase #2 $222.66   5.204%   $234.2472   $234.25   $234.25   $234.20  
  Purchase #3 $46.61   4.645%   $48.775   $48.78   $48.80   $48.80  
  Purchase #4 $54.81   13.730%   $62.3354   $62.34   $62.35   $62.30  
  Purchase #5 $28.80   11.239%   $32.0368   $32.04   $32.05   $32.00  
  Purchase #6 $190.78   3.268%   $197.0147   $197.01   $197.00   $197.00  
  Purchase #7 $222.60   4.846%   $233.3872   $233.39   $233.40   $233.40  
  7 purchase totals = $968.75       $1,023.3510   $1,023.36   $1,023.40   $1,023.30