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 $60.60   6.803%   $64.7226   $64.72   $64.70   $64.70  
  Purchase #2 $41.63   11.351%   $46.3554   $46.36   $46.35   $46.40  
  Purchase #3 $130.67   7.583%   $140.5787   $140.58   $140.60   $140.60  
  Purchase #4 $224.60   6.825%   $239.929   $239.93   $239.95   $239.90  
  Purchase #5 $39.91   3.828%   $41.4378   $41.44   $41.45   $41.40  
  Purchase #6 $216.54   6.727%   $231.1066   $231.11   $231.10   $231.10  
  Purchase #7 $232.83   8.564%   $252.7696   $252.77   $252.75   $252.80  
  7 purchase totals = $946.78       $1,016.8997   $1,016.91   $1,016.90   $1,016.90