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 $231.40   9.409%   $253.1724   $253.17   $253.15   $253.20  
  Purchase #2 $101.94   11.112%   $113.2676   $113.27   $113.25   $113.30  
  Purchase #3 $35.82   5.617%   $37.832   $37.83   $37.85   $37.80  
  Purchase #4 $140.88   4.122%   $146.6871   $146.69   $146.70   $146.70  
  Purchase #5 $141.85   3.359%   $146.6147   $146.61   $146.60   $146.60  
  Purchase #6 $9.69   11.309%   $10.7858   $10.79   $10.80   $10.80  
  Purchase #7 $105.49   3.679%   $109.371   $109.37   $109.35   $109.40  
  7 purchase totals = $767.07       $817.7306   $817.73   $817.70   $817.80