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 $227.94   12.680%   $256.8428   $256.84   $256.85   $256.80  
  Purchase #2 $217.59   8.391%   $235.848   $235.85   $235.85   $235.80  
  Purchase #3 $105.93   12.338%   $118.9996   $119.00   $119.00   $119.00  
  Purchase #4 $32.40   12.512%   $36.4539   $36.45   $36.45   $36.50  
  Purchase #5 $55.77   8.483%   $60.501   $60.50   $60.50   $60.50  
  Purchase #6 $241.31   8.449%   $261.6983   $261.70   $261.70   $261.70  
  Purchase #7 $52.70   13.734%   $59.9378   $59.94   $59.95   $59.90  
  7 purchase totals = $933.64       $1,030.2814   $1,030.28   $1,030.30   $1,030.20