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 $212.26   11.544%   $236.7633   $236.76   $236.75   $236.80  
  Purchase #2 $213.82   13.340%   $242.3436   $242.34   $242.35   $242.30  
  Purchase #3 $157.67   5.866%   $166.9189   $166.92   $166.90   $166.90  
  Purchase #4 $189.85   13.612%   $215.6924   $215.69   $215.70   $215.70  
  Purchase #5 $189.96   5.702%   $200.7915   $200.79   $200.80   $200.80  
  Purchase #6 $241.82   11.284%   $269.107   $269.11   $269.10   $269.10  
  Purchase #7 $232.98   10.699%   $257.9065   $257.91   $257.90   $257.90  
  7 purchase totals = $1,438.36       $1,589.5232   $1,589.52   $1,589.50   $1,589.50