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 $157.43   10.218%   $173.5162   $173.52   $173.50   $173.50  
  Purchase #2 $62.39   8.411%   $67.6376   $67.64   $67.65   $67.60  
  Purchase #3 $156.58   6.546%   $166.8297   $166.83   $166.85   $166.80  
  Purchase #4 $110.81   12.685%   $124.8662   $124.87   $124.85   $124.90  
  Purchase #5 $207.48   8.136%   $224.3606   $224.36   $224.35   $224.40  
  Purchase #6 $39.41   3.106%   $40.6341   $40.63   $40.65   $40.60  
  Purchase #7 $206.53   11.255%   $229.775   $229.78   $229.80   $229.80  
  7 purchase totals = $940.63       $1,027.6194   $1,027.63   $1,027.65   $1,027.60