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 $111.51   11.822%   $124.6927   $124.69   $124.70   $124.70  
  Purchase #2 $215.72   8.860%   $234.8328   $234.83   $234.85   $234.80  
  Purchase #3 $27.83   10.725%   $30.8148   $30.81   $30.80   $30.80  
  Purchase #4 $151.32   10.708%   $167.5233   $167.52   $167.50   $167.50  
  Purchase #5 $161.59   4.424%   $168.7387   $168.74   $168.75   $168.70  
  Purchase #6 $5.52   10.860%   $6.1195   $6.12   $6.10   $6.10  
  Purchase #7 $152.70   3.212%   $157.6047   $157.60   $157.60   $157.60  
  7 purchase totals = $826.19       $890.3265   $890.31   $890.30   $890.20