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 $185.73   11.795%   $207.6369   $207.64   $207.65   $207.60  
  Purchase #2 $23.26   7.153%   $24.9238   $24.92   $24.90   $24.90  
  Purchase #3 $44.28   13.530%   $50.2711   $50.27   $50.25   $50.30  
  Purchase #4 $250.64   12.468%   $281.8898   $281.89   $281.90   $281.90  
  Purchase #5 $143.75   4.697%   $150.5019   $150.50   $150.50   $150.50  
  Purchase #6 $188.64   6.396%   $200.7054   $200.71   $200.70   $200.70  
  Purchase #7 $120.81   5.732%   $127.7348   $127.73   $127.75   $127.70  
  7 purchase totals = $957.11       $1,043.6637   $1,043.66   $1,043.65   $1,043.60