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 $208.63   12.801%   $235.3367   $235.34   $235.35   $235.30  
  Purchase #2 $73.35   4.215%   $76.4417   $76.44   $76.45   $76.40  
  Purchase #3 $54.53   9.364%   $59.6362   $59.64   $59.65   $59.60  
  Purchase #4 $181.58   10.848%   $201.2778   $201.28   $201.30   $201.30  
  Purchase #5 $47.61   8.617%   $51.7126   $51.71   $51.70   $51.70  
  Purchase #6 $58.94   10.852%   $65.3362   $65.34   $65.35   $65.30  
  Purchase #7 $83.75   8.681%   $91.0203   $91.02   $91.00   $91.00  
  7 purchase totals = $708.39       $780.7615   $780.77   $780.80   $780.60