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 $56.52   3.763%   $58.6468   $58.65   $58.65   $58.60  
  Purchase #2 $140.68   4.452%   $146.9431   $146.94   $146.95   $146.90  
  Purchase #3 $117.40   10.804%   $130.0839   $130.08   $130.10   $130.10  
  Purchase #4 $49.77   5.592%   $52.5531   $52.55   $52.55   $52.60  
  Purchase #5 $245.51   6.845%   $262.3152   $262.32   $262.30   $262.30  
  Purchase #6 $24.69   10.331%   $27.2407   $27.24   $27.25   $27.20  
  Purchase #7 $17.83   4.563%   $18.6436   $18.64   $18.65   $18.60  
  7 purchase totals = $652.40       $696.4264   $696.42   $696.45   $696.30