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 $136.75   10.379%   $150.9433   $150.94   $150.95   $150.90  
  Purchase #2 $100.44   9.213%   $109.6935   $109.69   $109.70   $109.70  
  Purchase #3 $183.66   13.433%   $208.331   $208.33   $208.35   $208.30  
  Purchase #4 $246.76   9.258%   $269.605   $269.61   $269.60   $269.60  
  Purchase #5 $87.48   9.276%   $95.5946   $95.59   $95.60   $95.60  
  Purchase #6 $126.59   7.758%   $136.4109   $136.41   $136.40   $136.40  
  Purchase #7 $126.58   10.295%   $139.6114   $139.61   $139.60   $139.60  
  7 purchase totals = $1,008.26       $1,110.1897   $1,110.18   $1,110.20   $1,110.10