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 $12.52   12.619%   $14.0999   $14.10   $14.10   $14.10  
  Purchase #2 $237.81   13.218%   $269.2437   $269.24   $269.25   $269.20  
  Purchase #3 $169.66   9.868%   $186.402   $186.40   $186.40   $186.40  
  Purchase #4 $231.34   5.389%   $243.8069   $243.81   $243.80   $243.80  
  Purchase #5 $33.33   11.616%   $37.2016   $37.20   $37.20   $37.20  
  Purchase #6 $71.97   5.543%   $75.9593   $75.96   $75.95   $76.00  
  Purchase #7 $70.44   8.752%   $76.6049   $76.60   $76.60   $76.60  
  7 purchase totals = $827.07       $903.3183   $903.31   $903.30   $903.30