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 $66.34   12.588%   $74.6909   $74.69   $74.70   $74.70  
  Purchase #2 $222.71   9.261%   $243.3352   $243.34   $243.35   $243.30  
  Purchase #3 $35.74   6.305%   $37.9934   $37.99   $38.00   $38.00  
  Purchase #4 $56.91   11.681%   $63.5577   $63.56   $63.55   $63.60  
  Purchase #5 $248.78   5.587%   $262.6793   $262.68   $262.70   $262.70  
  Purchase #6 $225.57   11.163%   $250.7504   $250.75   $250.75   $250.80  
  Purchase #7 $77.72   11.190%   $86.4169   $86.42   $86.40   $86.40  
  7 purchase totals = $933.77       $1,019.4238   $1,019.43   $1,019.45   $1,019.50