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 $139.97   8.195%   $151.4405   $151.44   $151.45   $151.40  
  Purchase #2 $67.37   13.711%   $76.6071   $76.61   $76.60   $76.60  
  Purchase #3 $17.43   3.795%   $18.0915   $18.09   $18.10   $18.10  
  Purchase #4 $119.91   3.718%   $124.3683   $124.37   $124.35   $124.40  
  Purchase #5 $57.49   13.797%   $65.4219   $65.42   $65.40   $65.40  
  Purchase #6 $235.90   6.817%   $251.9813   $251.98   $252.00   $252.00  
  Purchase #7 $249.35   3.728%   $258.6458   $258.65   $258.65   $258.60  
  7 purchase totals = $887.42       $946.5564   $946.56   $946.55   $946.50