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 $208.93   8.514%   $226.7183   $226.72   $226.70   $226.70  
  Purchase #2 $38.34   13.793%   $43.6282   $43.63   $43.65   $43.60  
  Purchase #3 $244.36   5.716%   $258.3276   $258.33   $258.35   $258.30  
  Purchase #4 $26.83   9.415%   $29.356   $29.36   $29.35   $29.40  
  Purchase #5 $188.93   12.552%   $212.6445   $212.64   $212.65   $212.60  
  Purchase #6 $17.32   12.627%   $19.507   $19.51   $19.50   $19.50  
  Purchase #7 $106.28   4.672%   $111.2454   $111.25   $111.25   $111.20  
  7 purchase totals = $830.99       $901.4270   $901.44   $901.45   $901.30