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 $212.89   11.439%   $237.2425   $237.24   $237.25   $237.20  
  Purchase #2 $117.43   9.217%   $128.2535   $128.25   $128.25   $128.30  
  Purchase #3 $77.88   3.185%   $80.3605   $80.36   $80.35   $80.40  
  Purchase #4 $175.94   7.724%   $189.5296   $189.53   $189.55   $189.50  
  Purchase #5 $26.67   13.758%   $30.3393   $30.34   $30.35   $30.30  
  Purchase #6 $208.93   13.510%   $237.1564   $237.16   $237.15   $237.20  
  Purchase #7 $178.90   12.362%   $201.0156   $201.02   $201.00   $201.00  
  7 purchase totals = $998.64       $1,103.8974   $1,103.90   $1,103.90   $1,103.90