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 $223.53   8.653%   $242.8721   $242.87   $242.85   $242.90  
  Purchase #2 $139.93   11.187%   $155.584   $155.58   $155.60   $155.60  
  Purchase #3 $151.90   11.139%   $168.8201   $168.82   $168.80   $168.80  
  Purchase #4 $42.81   4.391%   $44.6898   $44.69   $44.70   $44.70  
  Purchase #5 $171.97   6.462%   $183.0827   $183.08   $183.10   $183.10  
  Purchase #6 $214.59   9.661%   $235.3215   $235.32   $235.30   $235.30  
  Purchase #7 $24.28   12.797%   $27.3871   $27.39   $27.40   $27.40  
  7 purchase totals = $969.01       $1,057.7573   $1,057.75   $1,057.75   $1,057.80