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 $219.75   6.557%   $234.159   $234.16   $234.15   $234.20  
  Purchase #2 $30.58   6.618%   $32.6038   $32.60   $32.60   $32.60  
  Purchase #3 $168.59   10.564%   $186.3998   $186.40   $186.40   $186.40  
  Purchase #4 $123.30   12.122%   $138.2464   $138.25   $138.25   $138.20  
  Purchase #5 $193.40   4.323%   $201.7607   $201.76   $201.75   $201.80  
  Purchase #6 $186.57   11.530%   $208.0815   $208.08   $208.10   $208.10  
  Purchase #7 $205.45   5.228%   $216.1909   $216.19   $216.20   $216.20  
  7 purchase totals = $1,127.64       $1,217.4421   $1,217.44   $1,217.45   $1,217.50