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 $235.51   5.859%   $249.3085   $249.31   $249.30   $249.30  
  Purchase #2 $86.75   6.861%   $92.7019   $92.70   $92.70   $92.70  
  Purchase #3 $225.60   4.358%   $235.4316   $235.43   $235.45   $235.40  
  Purchase #4 $158.77   5.148%   $166.9435   $166.94   $166.95   $166.90  
  Purchase #5 $167.56   11.382%   $186.6317   $186.63   $186.65   $186.60  
  Purchase #6 $56.38   5.800%   $59.65   $59.65   $59.65   $59.70  
  Purchase #7 $48.61   7.798%   $52.4006   $52.40   $52.40   $52.40  
  7 purchase totals = $979.18       $1,043.0678   $1,043.06   $1,043.10   $1,043.00