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 $200.26   10.231%   $220.7486   $220.75   $220.75   $220.70  
  Purchase #2 $22.81   7.819%   $24.5935   $24.59   $24.60   $24.60  
  Purchase #3 $246.60   13.610%   $280.1623   $280.16   $280.15   $280.20  
  Purchase #4 $29.92   9.266%   $32.6924   $32.69   $32.70   $32.70  
  Purchase #5 $237.30   3.331%   $245.2045   $245.20   $245.20   $245.20  
  Purchase #6 $109.38   4.453%   $114.2507   $114.25   $114.25   $114.30  
  Purchase #7 $214.41   10.118%   $236.104   $236.10   $236.10   $236.10  
  7 purchase totals = $1,060.68       $1,153.7560   $1,153.74   $1,153.75   $1,153.80