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 $166.56   11.230%   $185.2647   $185.26   $185.25   $185.30  
  Purchase #2 $249.86   5.229%   $262.9252   $262.93   $262.95   $262.90  
  Purchase #3 $186.59   8.162%   $201.8195   $201.82   $201.80   $201.80  
  Purchase #4 $158.30   11.336%   $176.2449   $176.24   $176.25   $176.20  
  Purchase #5 $66.73   3.451%   $69.0329   $69.03   $69.05   $69.00  
  Purchase #6 $250.52   6.850%   $267.6806   $267.68   $267.70   $267.70  
  Purchase #7 $230.37   9.740%   $252.808   $252.81   $252.80   $252.80  
  7 purchase totals = $1,308.93       $1,415.7758   $1,415.77   $1,415.80   $1,415.70