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 $144.95   12.301%   $162.7803   $162.78   $162.80   $162.80  
  Purchase #2 $217.41   3.753%   $225.5694   $225.57   $225.55   $225.60  
  Purchase #3 $198.94   5.379%   $209.641   $209.64   $209.65   $209.60  
  Purchase #4 $32.32   3.654%   $33.501   $33.50   $33.50   $33.50  
  Purchase #5 $65.87   12.750%   $74.2684   $74.27   $74.25   $74.30  
  Purchase #6 $227.87   9.445%   $249.3923   $249.39   $249.40   $249.40  
  Purchase #7 $79.92   7.871%   $86.2105   $86.21   $86.20   $86.20  
  7 purchase totals = $967.28       $1,041.3629   $1,041.36   $1,041.35   $1,041.40