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 $119.86   11.413%   $133.5396   $133.54   $133.55   $133.50  
  Purchase #2 $219.95   13.402%   $249.4277   $249.43   $249.45   $249.40  
  Purchase #3 $134.60   3.258%   $138.9853   $138.99   $139.00   $139.00  
  Purchase #4 $38.26   13.868%   $43.5659   $43.57   $43.55   $43.60  
  Purchase #5 $25.69   7.716%   $27.6722   $27.67   $27.65   $27.70  
  Purchase #6 $175.30   9.727%   $192.3514   $192.35   $192.35   $192.40  
  Purchase #7 $246.43   5.786%   $260.6884   $260.69   $260.70   $260.70  
  7 purchase totals = $960.09       $1,046.2305   $1,046.24   $1,046.25   $1,046.30