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 $214.76   9.539%   $235.246   $235.25   $235.25   $235.20  
  Purchase #2 $70.52   7.478%   $75.7935   $75.79   $75.80   $75.80  
  Purchase #3 $64.83   10.759%   $71.8051   $71.81   $71.80   $71.80  
  Purchase #4 $33.27   6.715%   $35.5041   $35.50   $35.50   $35.50  
  Purchase #5 $233.52   3.224%   $241.0487   $241.05   $241.05   $241.00  
  Purchase #6 $76.58   13.522%   $86.9351   $86.94   $86.95   $86.90  
  Purchase #7 $51.79   9.723%   $56.8255   $56.83   $56.85   $56.80  
  7 purchase totals = $745.27       $803.1580   $803.17   $803.20   $803.00