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 $61.69   12.826%   $69.6024   $69.60   $69.60   $69.60  
  Purchase #2 $27.97   11.762%   $31.2598   $31.26   $31.25   $31.30  
  Purchase #3 $52.53   10.433%   $58.0105   $58.01   $58.00   $58.00  
  Purchase #4 $172.55   6.741%   $184.1816   $184.18   $184.20   $184.20  
  Purchase #5 $192.58   10.822%   $213.421   $213.42   $213.40   $213.40  
  Purchase #6 $18.89   11.693%   $21.0988   $21.10   $21.10   $21.10  
  Purchase #7 $105.46   6.803%   $112.6344   $112.63   $112.65   $112.60  
  7 purchase totals = $631.67       $690.2085   $690.20   $690.20   $690.20