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 $64.65   3.828%   $67.1248   $67.12   $67.10   $67.10  
  Purchase #2 $234.72   7.433%   $252.1667   $252.17   $252.15   $252.20  
  Purchase #3 $71.91   4.185%   $74.9194   $74.92   $74.90   $74.90  
  Purchase #4 $23.87   11.410%   $26.5936   $26.59   $26.60   $26.60  
  Purchase #5 $75.44   5.616%   $79.6767   $79.68   $79.70   $79.70  
  Purchase #6 $157.49   6.680%   $168.0103   $168.01   $168.00   $168.00  
  Purchase #7 $206.86   8.356%   $224.1452   $224.15   $224.15   $224.10  
  7 purchase totals = $834.94       $892.6367   $892.64   $892.60   $892.60