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 $140.58   8.333%   $152.2945   $152.29   $152.30   $152.30  
  Purchase #2 $86.68   6.490%   $92.3055   $92.31   $92.30   $92.30  
  Purchase #3 $96.25   7.525%   $103.4928   $103.49   $103.50   $103.50  
  Purchase #4 $235.81   10.695%   $261.0299   $261.03   $261.05   $261.00  
  Purchase #5 $227.26   13.429%   $257.7787   $257.78   $257.80   $257.80  
  Purchase #6 $30.32   6.506%   $32.2926   $32.29   $32.30   $32.30  
  Purchase #7 $248.39   7.621%   $267.3198   $267.32   $267.30   $267.30  
  7 purchase totals = $1,065.29       $1,166.5138   $1,166.51   $1,166.55   $1,166.50