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 $56.90   8.153%   $61.5391   $61.54   $61.55   $61.50  
  Purchase #2 $174.65   8.845%   $190.0978   $190.10   $190.10   $190.10  
  Purchase #3 $248.63   11.546%   $277.3368   $277.34   $277.35   $277.30  
  Purchase #4 $10.71   10.822%   $11.869   $11.87   $11.85   $11.90  
  Purchase #5 $70.94   13.444%   $80.4772   $80.48   $80.50   $80.50  
  Purchase #6 $223.52   7.217%   $239.6514   $239.65   $239.65   $239.70  
  Purchase #7 $157.92   3.629%   $163.6509   $163.65   $163.65   $163.70  
  7 purchase totals = $943.27       $1,024.6222   $1,024.63   $1,024.65   $1,024.70