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 $91.94   5.232%   $96.7503   $96.75   $96.75   $96.80  
  Purchase #2 $246.32   12.240%   $276.4696   $276.47   $276.45   $276.50  
  Purchase #3 $212.30   4.602%   $222.07   $222.07   $222.05   $222.10  
  Purchase #4 $146.94   9.237%   $160.5128   $160.51   $160.50   $160.50  
  Purchase #5 $136.32   6.552%   $145.2517   $145.25   $145.25   $145.30  
  Purchase #6 $57.34   10.847%   $63.5597   $63.56   $63.55   $63.60  
  Purchase #7 $213.58   12.621%   $240.5359   $240.54   $240.55   $240.50  
  7 purchase totals = $1,104.74       $1,205.1500   $1,205.15   $1,205.10   $1,205.30