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 $249.47   6.191%   $264.9147   $264.91   $264.90   $264.90  
  Purchase #2 $227.98   9.667%   $250.0188   $250.02   $250.00   $250.00  
  Purchase #3 $67.61   9.398%   $73.964   $73.96   $73.95   $74.00  
  Purchase #4 $190.86   8.701%   $207.4667   $207.47   $207.45   $207.50  
  Purchase #5 $21.45   7.553%   $23.0701   $23.07   $23.05   $23.10  
  Purchase #6 $57.99   6.495%   $61.7565   $61.76   $61.75   $61.80  
  Purchase #7 $177.39   10.687%   $196.3477   $196.35   $196.35   $196.30  
  7 purchase totals = $992.75       $1,077.5385   $1,077.54   $1,077.45   $1,077.60