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 $249.47   13.145%   $282.2628   $282.26   $282.25   $282.30  
  Purchase #2 $211.38   6.321%   $224.7413   $224.74   $224.75   $224.70  
  Purchase #3 $54.41   10.138%   $59.9261   $59.93   $59.95   $59.90  
  Purchase #4 $67.52   8.291%   $73.1181   $73.12   $73.10   $73.10  
  Purchase #5 $212.58   10.553%   $235.0136   $235.01   $235.00   $235.00  
  Purchase #6 $208.70   10.731%   $231.0956   $231.10   $231.10   $231.10  
  Purchase #7 $26.41   13.615%   $30.0057   $30.01   $30.00   $30.00  
  7 purchase totals = $1,030.47       $1,136.1632   $1,136.17   $1,136.15   $1,136.10