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 $250.95   12.604%   $282.5797   $282.58   $282.60   $282.60  
  Purchase #2 $207.81   9.383%   $227.3088   $227.31   $227.30   $227.30  
  Purchase #3 $53.46   5.397%   $56.3452   $56.35   $56.35   $56.30  
  Purchase #4 $8.95   10.311%   $9.8728   $9.87   $9.85   $9.90  
  Purchase #5 $47.64   11.182%   $52.9671   $52.97   $52.95   $53.00  
  Purchase #6 $216.86   10.574%   $239.7908   $239.79   $239.80   $239.80  
  Purchase #7 $166.41   11.270%   $185.1644   $185.16   $185.15   $185.20  
  7 purchase totals = $952.08       $1,054.0288   $1,054.03   $1,054.00   $1,054.10