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 $206.90   12.440%   $232.6384   $232.64   $232.65   $232.60  
  Purchase #2 $176.77   13.681%   $200.9539   $200.95   $200.95   $201.00  
  Purchase #3 $127.88   8.792%   $139.1232   $139.12   $139.10   $139.10  
  Purchase #4 $171.92   7.285%   $184.4444   $184.44   $184.45   $184.40  
  Purchase #5 $120.48   9.733%   $132.2063   $132.21   $132.20   $132.20  
  Purchase #6 $23.91   11.720%   $26.7123   $26.71   $26.70   $26.70  
  Purchase #7 $238.43   5.680%   $251.9728   $251.97   $251.95   $252.00  
  7 purchase totals = $1,066.29       $1,168.0513   $1,168.04   $1,168.00   $1,168.00