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 $245.31   9.495%   $268.6022   $268.60   $268.60   $268.60  
  Purchase #2 $207.61   11.687%   $231.8734   $231.87   $231.85   $231.90  
  Purchase #3 $41.83   5.190%   $44.001   $44.00   $44.00   $44.00  
  Purchase #4 $122.96   9.649%   $134.8244   $134.82   $134.80   $134.80  
  Purchase #5 $154.84   8.827%   $168.5077   $168.51   $168.50   $168.50  
  Purchase #6 $225.66   12.341%   $253.5087   $253.51   $253.50   $253.50  
  Purchase #7 $222.74   4.648%   $233.093   $233.09   $233.10   $233.10  
  7 purchase totals = $1,220.95       $1,334.4104   $1,334.40   $1,334.35   $1,334.40