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 $245.93   11.848%   $275.0678   $275.07   $275.05   $275.10  
  Purchase #2 $243.37   3.103%   $250.9218   $250.92   $250.90   $250.90  
  Purchase #3 $101.52   9.814%   $111.4832   $111.48   $111.50   $111.50  
  Purchase #4 $25.63   4.552%   $26.7967   $26.80   $26.80   $26.80  
  Purchase #5 $172.80   13.365%   $195.8947   $195.89   $195.90   $195.90  
  Purchase #6 $119.95   13.699%   $136.382   $136.38   $136.40   $136.40  
  Purchase #7 $107.50   8.523%   $116.6622   $116.66   $116.65   $116.70  
  7 purchase totals = $1,016.70       $1,113.2084   $1,113.20   $1,113.20   $1,113.30