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 $183.41   11.601%   $204.6874   $204.69   $204.70   $204.70  
  Purchase #2 $230.83   8.331%   $250.0604   $250.06   $250.05   $250.10  
  Purchase #3 $209.66   9.831%   $230.2717   $230.27   $230.25   $230.30  
  Purchase #4 $8.90   9.539%   $9.749   $9.75   $9.75   $9.70  
  Purchase #5 $49.44   6.432%   $52.62   $52.62   $52.60   $52.60  
  Purchase #6 $51.50   4.827%   $53.9859   $53.99   $54.00   $54.00  
  Purchase #7 $139.95   8.733%   $152.1718   $152.17   $152.15   $152.20  
  7 purchase totals = $873.69       $953.5462   $953.55   $953.50   $953.60