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 $107.87   3.299%   $111.4286   $111.43   $111.45   $111.40  
  Purchase #2 $96.35   13.832%   $109.6771   $109.68   $109.70   $109.70  
  Purchase #3 $234.26   5.335%   $246.7578   $246.76   $246.75   $246.80  
  Purchase #4 $124.65   10.371%   $137.5775   $137.58   $137.60   $137.60  
  Purchase #5 $137.54   7.302%   $147.5832   $147.58   $147.60   $147.60  
  Purchase #6 $47.70   4.156%   $49.6824   $49.68   $49.70   $49.70  
  Purchase #7 $250.27   4.189%   $260.7538   $260.75   $260.75   $260.80  
  7 purchase totals = $998.64       $1,063.4604   $1,063.46   $1,063.55   $1,063.60