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 $230.79   13.351%   $261.6028   $261.60   $261.60   $261.60  
  Purchase #2 $43.33   7.108%   $46.4099   $46.41   $46.40   $46.40  
  Purchase #3 $57.93   6.137%   $61.4852   $61.49   $61.50   $61.50  
  Purchase #4 $149.75   7.553%   $161.0606   $161.06   $161.05   $161.10  
  Purchase #5 $212.72   3.266%   $219.6674   $219.67   $219.65   $219.70  
  Purchase #6 $228.69   10.422%   $252.5241   $252.52   $252.50   $252.50  
  Purchase #7 $172.78   11.724%   $193.0367   $193.04   $193.05   $193.00  
  7 purchase totals = $1,095.99       $1,195.7867   $1,195.79   $1,195.75   $1,195.80