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 $61.88   7.567%   $66.5625   $66.56   $66.55   $66.60  
  Purchase #2 $218.32   9.863%   $239.8529   $239.85   $239.85   $239.90  
  Purchase #3 $24.98   7.773%   $26.9217   $26.92   $26.90   $26.90  
  Purchase #4 $134.96   3.203%   $139.2828   $139.28   $139.30   $139.30  
  Purchase #5 $76.80   11.356%   $85.5214   $85.52   $85.50   $85.50  
  Purchase #6 $107.52   7.255%   $115.3206   $115.32   $115.30   $115.30  
  Purchase #7 $231.75   10.348%   $255.7315   $255.73   $255.75   $255.70  
  7 purchase totals = $856.21       $929.1934   $929.18   $929.15   $929.20