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 $86.92   10.548%   $96.0883   $96.09   $96.10   $96.10  
  Purchase #2 $32.40   5.564%   $34.2027   $34.20   $34.20   $34.20  
  Purchase #3 $151.52   7.435%   $162.7855   $162.79   $162.80   $162.80  
  Purchase #4 $73.94   5.231%   $77.8078   $77.81   $77.80   $77.80  
  Purchase #5 $159.89   9.453%   $175.0044   $175.00   $175.00   $175.00  
  Purchase #6 $122.27   7.576%   $131.5332   $131.53   $131.55   $131.50  
  Purchase #7 $196.48   13.451%   $222.9085   $222.91   $222.90   $222.90  
  7 purchase totals = $823.42       $900.3304   $900.33   $900.35   $900.30