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 $57.37   8.188%   $62.0675   $62.07   $62.05   $62.10  
  Purchase #2 $209.94   6.617%   $223.8317   $223.83   $223.85   $223.80  
  Purchase #3 $221.68   13.231%   $251.0105   $251.01   $251.00   $251.00  
  Purchase #4 $23.76   3.866%   $24.6786   $24.68   $24.70   $24.70  
  Purchase #5 $35.98   5.712%   $38.0352   $38.04   $38.05   $38.00  
  Purchase #6 $83.69   8.447%   $90.7593   $90.76   $90.75   $90.80  
  Purchase #7 $98.75   8.547%   $107.1902   $107.19   $107.20   $107.20  
  7 purchase totals = $731.17       $797.5730   $797.58   $797.60   $797.60