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 $154.62   6.660%   $164.9177   $164.92   $164.90   $164.90  
  Purchase #2 $33.67   11.581%   $37.5693   $37.57   $37.55   $37.60  
  Purchase #3 $218.70   8.818%   $237.985   $237.99   $238.00   $238.00  
  Purchase #4 $76.89   11.813%   $85.973   $85.97   $85.95   $86.00  
  Purchase #5 $202.61   9.694%   $222.251   $222.25   $222.25   $222.30  
  Purchase #6 $187.89   7.669%   $202.2993   $202.30   $202.30   $202.30  
  Purchase #7 $76.68   5.628%   $80.9956   $81.00   $81.00   $81.00  
  7 purchase totals = $951.06       $1,031.9909   $1,032.00   $1,031.95   $1,032.10